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MICHIGAN DESIGN MANUAL ROAD DESIGN

CHAPTER 3

INDEX

ALIGNMENT AND GEOMETRICS

3.01 REFERENCES

3.02 DEFINITION OF TERMS

3.03 ALIGNMENT - GENERAL A. Horizontal Alignment B. Vertical AlignmentC. Combined

3.03.01 Horizontal Alignment - Design Controls A. Minimum RadiusB. Minimum Curve LengthsC. Compound CurvesD. Sight DistancesE. Horizontal Curve Computations F. Spirals

3.03.02 Vertical Alignment - Design Controls A. Minimum / Maximum GradesB. Minimum Vertical Curve LengthsC. Stopping Sight Distance

D. DrainageE. Other ConsiderationsF. Computations

3.04 SUPERELEVATION AND CROSS SLOPES

3.04.01 Point of Rotation

3.04.02 Superelevation Transitions

3.04.03 Superelevation Using a Straight Line Method

3.05 Section Deleted

3.06 DESIGN SPEED

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CHAPTER 3 ALIGNMENT AND GEOMETRICS INDEX (cont inued)

3.07 GEOMETRICS

3.07.01 Lane Width, Capacity and Vehicle Characteristics A. Lane Width and CapacityB. Vehicle Characteristics

3.07.02 Interchange Geometrics A. Rural and UrbanB. Interchange LayoutC. Crossroads Over Freeways D. Ramp RadiiE. Single Lane Ramp Widths

3.07.03 Speed Change Lanes and Transitions

3.07.04 Intersections

3.08 3R, 4R AND OTHER PROJECTS

3.08.01 General A. (3R) Resurfacing Restoration and Rehabilitation B. (4R) New Construction/ReconstructionC. Combined 3R and 4R WorkD. Other Work CategoriesE. Design ExceptionsF. Safety Review / Crash Analysis

3.09 NON-FREEWAY RESURFACING, RESTORATION, AND REHABILITATION(3R) MINIMUM DESIGN GUIDELINES

3.09.01 General

3.09.02 3R Minimum Guidelines A. Non-Freeway, NHSB. Non-Freeway, Non-NHS C. Design ExceptionsD. Section DeletedE. Vertical CurvesF. Horizontal Curves

3.09.03 3R Non-Freeway Safety Considerations A. SigningB. Evaluation of Guardrail and Bridge RailC. Tree RemovalD. Roadside ObstaclesE. Cross Section Elements

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3.09.04 Bridges

3.09.05 Guidelines for Passing Relief Lanes A. GeneralB. Truck Climbing LanesC. Passing Lane Sections

3.10 NON-FREEWAY RECONSTRUCTION / NEW CONSTRUCTION (4R)

3.10.01 General

3.10.02 Design Criteria

3.10.03 Design Exceptions

3.11 FREEWAY RESURFACING, RESTORATION, REHABILITATION ANDRECONSTRUCTION / NEW CONSTRUCTION (3R/4R) DESIGN CRITERIA

3.11.01 General

3.11.02 Freeway 3R/4R Checklist A. Section DeletedB. Geometrics and SigningC. Section DeletedD. Design Exceptions

3.11.03 Safety Considerations A. Section DeletedB. Ramp Geometrics and Taper LengthsC. Vertical CurbsD. Sight DistancesE. Crown Location/Pavement Cross SlopeF. SuperelevationG. Guardrail and Concrete BarrierH. AttenuationI. Shoulder Cross SlopesJ. Section Deleted (information moved to Section 3.12) K. Clear Zones & Fixed ObjectsL. Culvert End Treatments

M. Bridges

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3.12 UNDERCLEARANCES

A. 4R FreewayB. 4R ArterialsC. 4R Collectors and Local RoutesD. 3R FreewayE. 3R ArterialsF. Preventative MaintenanceG. Vertical Clearance Requirement TableH. Design Exception Requirements for Vertical Clearance

Appendix 3A Geometr ic Design Elements – New Construc tion / Reconst ruct ion

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CHAPTER 3

ALIGNMENT AND GEOMETRICS

3.01 (revised 2006)

REFERENCES

A. A Policy on Design Standards -Interstate System, AASHTO, 2005

B. A Pol icy on Geometr ic Design ofHighways and Streets, AASHTO, 2004

C. Highway Capacity Manual, 2000,published by Transportation ResearchBoard, National Research Council.

D. MDOT Geometric Design Guides

E. Michigan Manual of Uniform TrafficControl Devices, current edition, by theMichigan Department of Transportation

F. Roadside Design Guide, AASHTO, 2006

G. Standard Plan R-107-Series,Superelevation and Pavement Crowns

H. MDOT Sight Distance Guidelines

3.02 (revised 8-17-2009)

DEFINITION OF TERMS

Accelerat ion Lane - An auxiliary lane,including tapers, for the acceleration ofvehicles entering another roadway.

Ar ter ial Road – A roadway which provides ahigh speed, high volume, network for travelbetween major points.

Auxi liary Lane – Portion of the roadwayadjoining the traveled way for speed change,turning, storage for turning, weaving, truckclimbing, passing and other purposessupplementary to through-traffic movement.

Average Dail y Traf fic (ADT) - The average24 hour traffic volume, based on a yearly total.

Broken Back Curve - Two curves in thesame direction joined by a short tangentdistance.

Compound Curve - Two connectinghorizontal curves in the same direction havingdifferent radii.

Collector Road – Roadway linking a LocalRoad to an Arterial Road, usually servingmoderate traffic volumes.

Crash Analysis - A site specific safety reviewof crash data performed to identify whether ornot a specific geometric design element haseither caused, or contributed, to a pattern orconcentration of crashes at the location inquestion. The analysis is a critical componentused in determining the appropriateapplication of geometric design criteria and inthe evaluation of design exception approvalrequests.

http://mdotcf.state.mi.us/public/tands/Details_Web/mdot_%20sight_distance_guidelines.pdf




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VOLUME 3 MICHIGAN DESIGN MANUAL ROAD DESIGN

3.02 (continued)

DEFINITION OF TERMS

Critical Grade - The grade and length thatcauses a typical truck or other heavy vehicleto have a speed reduction of 10 mph orgreater.

Cross Slope – Transverse slope rate oftraveled lane or shoulder.

Cross Slope Break - Algebraic difference inrate of adjacent lane cross slopes havingslopes in same direction (eg., between thru

lanes or thru and auxiliary lanes).

Crown Line Crossover – The algebraicdifference in rate of adjacent lane crossslopes at the crown point.

Crown Runout - (also called TangentRunout) - The distance necessary to removeadverse crown before transitioning intosuperelevation on curves. (Referred to as “C”distance in Standard Plan R-107-Series.)

Deceleration Lane - An auxiliary lane thatenables a vehicle to slow down and exit thehighway with minimum interference fromthrough traffic.

Design Hour Volume (DHV) - The hourlyvolume used to design a particular segment ofhighway.

Directional Design Hour Volume (DDHV) -The directional distribution of traffic during theDHV.

Free Access Highway - A highway, with nocontrol of access, usually having at-gradeintersections, which may or may not bedivided.

Freeway - A divided arterial highway with fullcontrol of access and grade separations atintersections.

3.02 (continued)

Gore Area - The "V" area immediately beyond

the convergence or divergence of tworoadways bounded by the edges of thoseroadways.

Grade Separation - A structure that providesfor highway traffic to pass over or underanother highway or the tracks of a railway.

Horizontal Clearance – An operational offsetproviding clearance for external vehiclecomponents such as mirrors on trucks andbuses and for opening curbside doors of

parked vehicles. A minimum 1’-6" horizontalclearance from the face of curb to anobstruction is required on curbed roadways. Ifthe roadway and curb are separated by ashoulder, the shoulder width is included aspart of the clearance. Interchange - A system of interconnectingroadways in conjunction with gradeseparations providing for the interchange oftraffic between two or more intersectingroadways.

Level of Service - A qualitative measuredescribing operational conditions within atraffic stream; generally described in terms ofsuch factors as speed and travel time,freedom to maneuver, traffic interruptions,comfort and convenience, and safety. Levelsof service are given letter designations, from Ato F, with LOS A representing the bestoperating conditions and LOS F the worst.

Local Road – A road which serves primarilyto provide access to farms, residences,business, or other abutting properties.

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3.02 (continued)

DEFINITION OF TERMS

Passing Lane Section (PLS) - Extra lane(s)to provide additional capacity and reducedelay caused by slow moving vehicles, suchas recreational vehicles, during peak periods.These are often desirable in areas whereslower vehicles are not necessarily the resultof long steep grades.

Passing Relief Lane (PRL) - Common,all-inclusive reference to a traffic laneprovided for increased passing opportunities

along a route, can be a Truck Climbing Lane(TCL) or a Passing Lane Section (PLS).

Ramp - A connecting roadway between twointersecting roadways, usually at gradeseparations.

Reverse Curve – Horizontal curves in theopposite direction joined by a short tangentdistance or common point.

Roll-over - Algebraic difference in rate ofcross slope between traveled lane and

shoulder.

Safety Review - A general safety review of aproject performed to identify potential safetyenhancements within the limits of a proposed3R or 4R project.

Service Road (also Frontage Road) - Aroadway usually parallel and adjacent to ahighway which provides access to abuttingproperties by separating local and throughtraffic.

Sight Distance - The unobstructed distancethat can be viewed along a roadway - usuallyreferenced to decision points for drivers.

3.02 (continued)

Spiral Curve Transition - A variable radiicurve between a circular curve and thetangent. The radii of the transition and thecurve are the same at the curve and increaseto infinity at the tangent end of the transition.

Superelevation – The banking of theroadway in the direction of the curve to helpcounter balance the centrifugal force on thevehicle.

Superelevation Transition (sometimesreferred to as superelevation runoff) – The

distance needed to change the pavementcross slope in the direction of the curve from asection with adverse crown removed to a fullysuperelevated section, or vice versa.(Referred to as “L” distance in Standard PlanR-107-Series.)

Truck Climbing Lane (TCL) - An extra lanefor heavy vehicles slowed by the presence ofa long steep “critical grade”, that providespassing opportunities for non-slowed vehicles.

Vehicles Per Hour (vph) - A measurement of

traffic flow.

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3.03 (revised 1-23-2012)

ALIGNMENT-GENERAL

The geometric design of a roadway consistsof horizontal alignment, vertical alignment,and a combination of the two. A properlydesigned alignment (horizontal and vertical)leads to the safe and efficient movement oftraffic.

A. Hor izontal Alignment

Horizontal alignment is a major factor indetermining safety, driving comfort, and

capacity of a highway.

Some important factors to consider whendesigning for horizontal alignment:

1. Passing sight distance on two-lane,two-way roadways should be maximized.

2. Curves should be as flat as physicalconditions permit. Abrupt changes inalignment introduce the element ofsurprise to the driver and should beavoided.

3. Broken back curves should be avoidedbecause they are unsightly and driversdo not expect succeeding curves to be inthe same direction.

4. If possible, the minimum distancebetween reverse curves should be thesum of the superelevation transitions,outside the curves, plus the crown runoutlengths. The crown runout can beeliminated in some situations. See the

Geometrics Unit (Design Division) foradditional guidance. When it isn'tpossible to obtain the desired distancebetween reverse curves, up to 40% ofthe transition may be placed in thecurves.

3.03 (continued) B. Vertical Alignment

Vertical alignment establishes the profilegrade of a proposed road construction project.The grade can be over virgin land as in thecase of a relocation project or along anexisting roadway, as in the case of aresurfacing project. In either case and in mostproposed construction projects, a profile gradeshould be established.

Obviously a profile grade must always beestablished for new construction or relocation

projects. Most reconstruction andrehabilitation projects will require new profilegrades if improvements for sight distance,superelevation, and drainage are included. Asimple resurfacing project can usually beconstructed without establishing a new verticalalignment.

Establishing the vertical alignment is based onmany factors, including terrain, existingconditions, soils, drainage, coordination withthe horizontal alignment, location of bridges,culverts, crossroads, design speed, earthwork

balance, etc. The Designer must work withavailable resources such as the GeometricsUnit of the Design Division to provide the bestpossible vertical alignment. The final productshould be safe, functional, aestheticallypleasing, and economical.

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3.03 (continued)

ALIGNMENT-GENERAL

C. Combined

Horizontal and vertical alignments arepermanent design elements. It is extremelydifficult and costly to correct alignmentdeficiencies after the highway is constructed.

A proper combination of horizontal andvertical alignment is obtained by engineeringstudy using the following general controls.

1. Vertical curvature superimposed onhorizontal curvature, generally results ina more pleasing appearance.Successive changes in profile not incombination with horizontal curvaturemay result in a series of humps visible tothe driver for some distance.

2. Sharp horizontal curvature should not beintroduced at or near the top of apronounced crest vertical curve. Thiscondition may make it difficult for thedriver to perceive the horizontal changein alignment. This can be avoided if the

horizontal curvature leads the verticalcurvature, i.e., the horizontal curve ismade longer than the vertical curve.

3. Sharp horizontal curvature should not beintroduced at or near the low point of apronounced sag vertical curve. Becausethe road ahead would appear to be fore-shortened, a relatively "flat" horizontalcurve should be used to avoid thisundesirable phenomenon.

4. Horizontal curvature and profile should

be made as flat as possible atintersections where sight distance alongboth roads or streets is important.

See Chapter 3 of A Policy on GeometricDesign of Highways and Streets, AASHTO,2004 for elements of design.

3.03.01 (revised 10-21-2013)

Horizontal Alignment - Design Controls

A. Minimum Radius

The minimum radius is a limiting value ofcurvature for a given design speed and isdetermined from the maximum rate ofsuperelevation and the maximum side frictionfactor. The minimum radius of curvatureshould be avoided wherever practical. Attemptto use flatter curves, saving the minimumradius for the most critical conditions. Theminimum radius (Rmin) is shown in the

Standard Plan R-107-Series superelevationtabulation at the bottom of each column foreach design speed. Values for Rmin are alsotabulated for the straight line superelevationtable in Section 3.04.03.

B. Minimum Curve Lengths

Curves should be sufficiently long for smalldeflection angles to avoid the appearance of akink.

Curves on rural free access trunklines should

be at least 500 feet long for a central angle of5° and the minimum length should beincreased 100 feet for each 1° decrease in thecentral angle. The minimum should beapproximately 15 times the design speed witha desirable length of at least 30 times thedesign speed. For example a design speed of60 mph multiplied by 15 gives a minimumcurve length of 900’.

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3.03.01 (continued)


C. Compound Curves

Compound curves should be used withcaution. Although compound curves giveflexibility to fitting the highway to the terrainand other controls, designers should avoidthem whenever possible. When curves withconsiderably different radii are located tooclose together, the alignment will not have apleasing appearance. On one-way roadssuch as ramps, the difference in radii of

compound curves is not so important if thesecond curve is flatter than the first. Oncompound curves for open highways, the ratioof the flatter radius to the sharper radiusshould not exceed 1.5 to 1. On ramps theratio of the flatter radius to the sharper radiusmay be increased to a 2 to 1 ratio.

D. Sight Distances

Both stopping sight distance and passing sightdistance must be considered for two-wayroadways. On one-way roadways only

stopping sight distance is required. Thedesigner must be aware that both horizontaland vertical alignments need to be consideredwhen designing for sight distance.

From Exhibit 3-1 of A Pol icy on Geometr icDesign of Highways and Streets, AASHTO,2004 stopping sight distance can bedetermined from design speed.

Design SpeedStopping Sight Distance

(Design)

25 155

30 200

35 250

40 305

45 360

50 425

55 495

60 570

65 645

70 730

75 820

3.03.01 (continued)

For general use in the design of a horizontalcurve, the sight line is a chord of the curveand the stopping sight distance is measuredalong centerline of the inside lane around thecurve

Knowing the stopping sight distance (SSD)and the radius of curve (R) the horizontal

sightline offset (HSO) can be calculated from:

)R

28.65SSDcos-(1RHSO

or to verify that SSD is met for a given HSO:

28.65

)R

HSO-(1Rcos

SSD

1-

(R, SSD, HSO measured in feet)

These equations are exact only when thevehicle and sight obstruction are within thelimits of a circular curve.

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3.03.01 (continued)


When determining sight distances, use APolicy on Geometric Design of Highwaysand Streets, AASHTO. The MDOT SightDistance Guidelines also provide detailedinformation on sight distance calculation.

The four types of sight distances given arestopping, passing, decision, and intersection.

1. Stopping Sight Distance is defined as thesight distance available on a roadway that

is sufficiently long to enable a vehicletraveling at or near the design speed tostop before reaching a stationary object inits path.

2. Passing Sight Distance is defined as thelength needed to complete a passingmaneuver as described in A Pol icy onGeometric Design of Highways andStreets, AASHTO.

3. Decision Sight Distance is the distancerequired for a driver to detect an

unexpected or otherwise difficult-to-perceive information source or condition ina roadway environment that may bevisually cluttered, recognize the situationor its potential threat, select anappropriate speed and path, and initiateand complete the required maneuversafely and effectively.

3.03.01 (continued)

4. Intersection Sight Distance is the distance

that allows drivers sufficient view from aminor road to safely cross or turn on amajor road.

Generally 7.5 seconds of entering sightdistance is used for passenger vehiclesstopped on a minor road grade of 3% orless to turn left onto a two-lane roadway.

An additional 0.5 seconds is added foreach additional lane

Adjustments for other varying conditions

that may increase or decrease the timegap are provided in A Pol icy onGeometric Design of Highways andStreets, AASHTO.

The designer is cautioned that theelement of Clear vision for at-gradeintersections is very important, for safetyreasons, particularly on high speedtrunklines.






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3.03.01


E. Horizontal Curve Computations

∆ = Deflection or Central Angle (Delta), degrees

R = Radius of Curve, ft

T = Length of Tangent (P.C. to P.I.or P.I. to P.T.) = R Tan (∆/2), ft

E = External Distance =R [Sec (∆/2) - 1] or T Tan (∆/4), ft

M = Middle Ordinate Distance =R Versine (∆/2) or E Cos (∆/2), ft

L = Length of Curve = ∆ x R ÷ 57.2958, ft

P.C. = Point of Curvature

P.I. = Point of Intersection of Tangents

P.O.C.T. = Point on Curve Tangent

P.T. = Point of Tangency

D = Degree of Curvature =

R

5729.58degrees

(ft)

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3.03.01


F. Spirals

Spiral curves are used to transition intocircular curves and should be used on newalignments based on the design speed andradius of the curve, as shown on the table inStandard Plan R-107-Series. Spiral curvelengths are normally equal to thesuperelevation transition length. Therelationship between the various elements ofspiral curves and their methods of

computation are shown below and on thefollowing pages.

Usually the P.I. station and the deflectionangle (∆) are established. The spiral length(Ls) equals the length of superelevationrunoff; appropriate values for (Ls) can beobtained using Standard Plan R-107-Series.The remaining curve data can then becomputed or read from the tables of spiralcurve functions found in the ConstructionManual.

T.S. Sta. = P.I. Sta. - T (Sta.)S.C. Sta. = T.S. Sta. + Ls (Sta.)C.S. Sta. = T.S. Sta. + Ls (Sta.)+ Lcc (Sta.)S.T. Sta. = T.S. Sta. + 2Ls (Sta.) + Lcc (Sta.)

The radius of Central Angle (R) should bespecified to the nearest 15 feet; all other curvedata will be calculated and shown to thenearest one-hundredth of a foot or to thenearest second, whichever is applicable.

P.I. = Point of IntersectionT.S. = Tangent to SpiralS.C. = Spiral to CurveC.S. = Curve to SpiralS.T. = Spiral to Tangent

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3.03.01F (continued)


LEGEND AND FORMULAS FOR SPIRALS

sSin

YV

Δ=

sCotY-XU Δ= R

Ls28.6479s =Δ

s2cc Δ+Δ=Δ For ∆s Between Zero and 5°

3

sSinLsY

Δ=

2Ls

Y-LsX

2

=

4

YP =

2

XK =

R =

T =

Tcc =

U =

V =

Ls =

Lcc =

∆ =

∆cc =

∆s =

E =

Ecc =

X,Y =

K,P =

Radius of Central Angle, ft

Tangent Length of Entire Curve, ft

Tangent Length of Central Curve, ft

Long Tangent Length of Spiral, ft

Short Tangent Length of Spiral, ft

Spiral Length, ft

Central Curve Length, ft

Deflection Angle of Entire Curve, degrees

Deflection Angle of Central Curve, degrees

Deflection Angle of Spiral, degrees

External of Entire Curve, ft

External of Central Curve, ft

Coordinates of S.C. (or C.S.) , ft

Coordinates of Offset P.C. Referencedthe Same as X & Y, ft

)2

s(SecPThrow

Δ=

K2

TanP)(RT +Δ

+= P

4 Tan

2TanP)(RE +

ΔΔ+=

T and E may be computed from tables of unit length spiralsby taking the corresponding T & E values of the requireddeflection angle and multiplying them by Ls.

For ∆s Between 5° and 15° 12

sSinLsP

Δ=

Y 4P=

Ls

4P-

2

Ls K

2

= sSinRKX Δ+=

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3.03.02 (revised 11-28-2011)

Vertical Alignment – Design Controls

Vertical curves are in the shape of a parabola.The basic equation for determining theminimum vertical curve length is:

KAL =

WHERE:

L = length of vertical curve, feetK = horizontal distance to produce 1%

change in gradient, feet A = Algebraic difference between the twotangent grades, percent

(Refer to AASHTO's A Pol icy of Geometr icDesign for Roads and Streets for additionalVertical Curve Formulas). Also ref er to theMDOT Sight Distance Guidelines for moredetailed information on sight distancecalculation.

3.03.02 (continued)

A. Minimum / Maximum Grades

See the “Grade” section of Appendix 3A, theGeometric Design Elements table.

B. Minimum Vertical Curve Lengths

Minimum length (in feet) of a vertical curveshould be three times the design speed inmph.





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3.03.02 (continued)

Vertical Alignment – Design Controls

C. Stopping Sight Distance

Stopping Sight Distance (SSD) is the principalcontrol of the design of both crest and sagvertical curves. AASHTO's A Pol icy onGeometric Design of Highways and Streets gives values for K and lengths of verticalcurves for various operational conditions.Values based on reduced design speeds maybe used on non-freeway 3R projects.Minimum design guidelines for non-freeway

3R projects are presented in Section 3.09.02.The design speed used for a ramp verticalalignment should meet or exceed the designspeed used f or the ramp horizontal alignment.See MDOT Sight Distance Guidelines formore detailed information on sight distancecalculation.

D. Drainage

Minimum grades correlate with adequatedrainage. A desirable minimum grade istypically 0.5%, but grades of 0.3% may be

used for paved roadways. On curbedroadways, when it is necessary to use gradesthat are flatter than 0.3%, provide encloseddrainage with compensating decreased inletspacing. In addition, close attention to inletspacing is critical for sag and crest verticalcurves when the K value (rate of gradechange) is greater than 167.

Uncurbed roads with ditch drainage can havea level longitudinal grade if the crownadequately drains the pavement. Independent

ditches should be used when the grade is lessthan 0.3%. However, efforts to achieveminimum roadway grades of 0.5% would be ofgreat benefit in the event that future curb andgutter or concrete barrier may be installed.

3.03.02 (continued)

E. Other Considerations

Comfort criteria is sometimes a considerationfor sag vertical curves. The equation forlength of curve for comfort is:

46.5

AVL

2

=

WHERE:

L = length of vertical curve, feet

A = algebraic difference of tangent grades,percent

V = design speed, mph

Passing sight distance must be considered ontwo way roadways. Passing sight distance isthe distance required for a motorist to safelyperform a passing maneuver as described in

AASHTO.

Intersection Sight Distance is the distancethat allows drivers sufficient view from a

minor road to safely cross or turn on a majorroad. See Section 3.03.01.D4.

F. Computations

The following pages show mathematicaldetails used in the design of vertical curves.This section includes definitions, formulas,and examples.




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Computations

ELEMENT ABBREVIATION DEFINITION

Vertical Point of Curvature VPC The point at which a tangent grade ends andthe vertical curve begins.

Vertical Point of Tangency VPT The point at which the vertical curve endsand the tangent begins.

Vertical Point of Intersection VPI The point where the extension of two tangentgrades intersect.

Grade G1G2 The rate of slope between two adjacentVPI’s expressed as a percent. Thenumerical value for percent of grade is thevertical rise or fall in feet for each 100 feet ofhorizontal distance. Upgrades in thedirection of stationing are identified asplus (+). Downgrades are identified asminus (-).

External Distance E The vertical distance (offset) between theVPI and the roadway surface along the

vertical curve.

Algebraic Difference in Grade A The value A is determined by the deflectionin percent between two tangent grades.

Length of Vertical Curve L The horizontal distance in feet from the VPCto the VPT.

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Computations

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3.04 (revised 2006)

SUPERELEVATION ANDCROSS SLOPES

The maximum rate of superelevation isdetermined from the design speed, curveradii, and the maximum allowable side frictionfactor.

Michigan, because of its climate, limitssuperelevation to 7% maximum on ruralfreeways, free access trunklines, and ruralramps. For maximum superelevation onurban freeways and urban ramps see

Standard Plan R-107-Series.

Standard Plan R-107-Series (7% Emax) is thepreferred method for obtaining superelevationrates. Please note that interpolating betweenthe AASHTO 6% and 8% Emax charts to obtainan estimated value for 7% Emax criteria is notappropriate. Standard Plan R-107-Seriesshould be used. When it is not possible touse the rates provided in Standard PlanR-107-Series, the straight line method may beused on a curve by curve basis as needed.See Section 3.04.03. This method employs adistribution that generally produces moremoderate superelevation rates and uses amaximum rate of superelevation of 6%. If, asa maximum the straight line method cannot bemet, a design exception will be required.

3.04 (continued)

The department uses a standard cross slope

of 2% as shown on Standard PlanR-107-Series and Appendix 3A GeometricDesign Elements. See Section 6.09 for moreinformation on pavement crowns and crossslope. Also refer to Section 3.09.02 for crossslopes allowable on 3R Projects. A designexception is required when minimum crossslopes are not met and/or when pavementcross slopes exceed 2% except as statedbelow.

Cross slopes up to and including 2% are

barely perceptible in terms of vehicle steering. A maximum cross slope of 2% should be usedon the two lanes adjacent to the crownline.This will translate to crownline crossover of4%.

When three or more lanes are inclined in thesame direction on free access curbedhighways, each successive lane or portionsthereof, outward from the first two lanesadjacent to the crown line, may have anincreased slope. The cross slope rate may beincreased up to 1%. This helps facilitate

parabolic crown modifications when existingside conditions do not allow the preferreduniform standard crown rate. This use ofmultiple crown rates requires additionaltransition in superelevated sections. Seesketch below.

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3.04.01 (revised 2006)

Point of Rotation

Superelevation may be obtained by rotatingabout the center or about inside or outsidepavement edge profiles. Currently ourcrowned two-way and two-lane roadways arerotated about the pavement centerline perStandard Plan R-107-Series. This methodreduces the edge distortion because therequired change in elevation is distributedalong both pavement edges rather than all onone edge. Uncrowned or straight cross slopepavements, such as ramps, are rotated aboutthe alignment edge. Special considerationshould be given to superelevating widerpavements (i.e., three-lane or five-lanesections) as the point of rotation should bedetermined by site conditions. See StandardPlan R-107-Series.

3.04.02 (revised 2-18-2009)

Superelevation Transitions

The superelevation transition consists of thesuperelevation runoff (or transition (L) ) andtangent runout (or crown runout (C) ). Thesuperelevation runoff section consists of thelength of roadway needed to accomplish achange in outside-lane cross slope from zero(flat) to full superelevation, or vice versa. Thesuperelevation runoff is determined by thewidth of pavement (w), superelevation rate(e), and the relative gradient along the edgesof pavement (Δ%). As indicated in StandardPlan R-107-Series, one third of thesuperelevation runoff length is located in thecurve. When this can not be achieved, theportion of runoff located in the curve may beincreased to not more than 40%. The tangentrunout section consists of the length ofroadway needed to accomplish a change inoutside-lane cross slope from the normalcross slope rate to zero (flat), or vice versa.The tangent runout is determined by the widthof payment (w), normal cross slope/normalcrown (N.C.), and the relative gradient.Relative gradient values correspond to the

superelevation rates. The gradient may beincreased as needed up to the maximumrelative gradient for the design speed. Adesign exception is required for valuesexceeding the maximum relative gradient.

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3.05

Section deleted.

3.06 (revised 5-28-2013)

DESIGN SPEED

Design speed is a selected speed used todetermine the various geometric designfeatures of the roadway. Once selected, all ofthe pertinent design features of the highwayshould be related to the design speed toobtain a balanced design.

Design speeds shown in Appendix 3A areapplicable for 4R projects. The design speedused for freeway 3R projects (interstate andnon-interstate) may be the design speedapproved at the time of original construction orreconstruction, whichever is most recent. Thedesign speeds used for non-freeway 3Rprojects are shown in Section 3.09.02. SeeSection 3.08.01C f or information on combined3R and 4R work.

It is MDOT practice under most circumstancesto design roadway geometrics based on arecommended project design speed 5 mphgreater than the posted speed (See Appendix 3A, Geometric Design Elements and Section3.09.02A, 3R Minimum Guidelines, Non-Freeway NHS). This practice is founded inresearch that shows actual operating speedsare typically greater than the posted speeds.Posted speed is generally used as projectdesign speed only for non-freeway, non-NHS3R design (Section 3.09.02B). The designershould strive to meet the standards for all

geometric elements based on the prescribedMDOT recommended design speeds. This isthe project design speed to be recorded onthe title sheet.

3.06 (continued)

Design elements not meeting standards

based on MDOT recommended designspeeds require a Safety Review, Crash

Analysis and documented justification (useDesign Exception Form FC26). If the highestattainable design corresponds to criteria forspeeds less than the posted speed (exceptwhere permitted in Section 3.09.02B for non-NHS 3R), a design exception must besubmitted to the Engineer of Design Programsfor approval. For additional information seeSection 14.11.

For designs meeting criteria for a speedgreater than or equal to the posted speed butless than MDOT recommended design speed,the project manager must still document thebasis for not meeting standards for MDOTrecommended design speed. This internaldocumentation (including Form FC26 signedby the Project Manager, Safety Review andCrash Analysis) must be retained in theproject files and in the final documentretention when closing out the project files. Acopy of the documentation must also be sentto the Design Division’s Geometrics Unit.

It should be indicated on Form FC26 ifsubsequent approval by the Engineer ofDesign Programs is required or if thedocumentation is for file retention only.

Documentation must be for each geometricelement and not a blanket statement applyingto all geometric elements. A design speedreduction for individual geometric elementsdoes not redefine the overall “project designspeed”.

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3.07

GEOMETRICS

3.07.01 (revised 11-28-2011)

Lane Width, Capacity andVehicle Characteristics

A. Lane Width and Capacity

The lane width of a roadway greatly influencesthe safety and comfort of driving. See

Appendix 3A for lane width information for 4Rwork and Section 3.09.02 f or 3R work.

B. Vehicle Characteristics

There are two general classes of vehicles:passenger and commercial (trucks). Thegeometric design requirements for trucks andbuses are much more severe than they are forpassenger vehicles. Consult the GeometricsUnit in the Design Division for the appropriatedesign vehicle to be used on the job.Intersection radii for various types ofcommercial vehicles are given on Geometric

Design Guide GEO-650-Series, "Flares andIntersection Details". Also, for short radiiloops, additional ramp width may be neededto accommodate these vehicles. Generally,the Michigan WB-62 is the design vehicle tobe used in determining the radii to be used inturning movements at trunkline to trunklineintersections and interchanges.

Acceleration and deceleration rates ofvehicles are often critical in determininghighway design. These rates often govern thedimensions of design features such as

intersections, freeway ramps, speed changelanes, and climbing or passing lanes.

3.07.02 (revised 11-28-2011)

Interchange Geometrics

General: Contact the Geometrics Unit in theDesign Division for the recommendations /requirements of all geometric features ofhighway facilities.

A. Rural and Urban

Geometric Design Guides, developed by theGeometrics Unit in the Design Division showapproved criteria for ramp and interchangedesign. See Geometric Design Guides.

B. Interchange Layout

The following items should be considered inconjunction with the Geometric Design Guidesfor interchange design.

1. Exit ramps should be designed foradequate visibility for the motorist exitingthe freeway. Sight distance along a rampshould be at least as great as the designstopping sight distance. There should be aclear view of the entire exit terminal,

including the exit nose and a section ofthe ramp roadway beyond the gore.

2. Exit ramps should begin where thefreeway is on a tangent, when possible.

3. Drivers prefer and expect to exit inadvance of the structure. Loop ramps thatare located beyond the structure, usuallyneed a parallel deceleration lane.

4. Left-hand entrances and exits are contrary

to the concept of driver expectancy.Therefore, extreme care should beexercised to avoid left-hand entrances andexits in the designing of interchanges.

5. The geometric layout of the gore area ofexit ramps should be clearly seen andunderstood by the approaching drivers.

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3.07.02B (continued)


6. The cross slope in the gore area betweenthe 2’ point and the 22’ point should notexceed 8%, with a 6% maximum algebraicdifference in grades between the gore andthe adjacent lane. The 6% algebraicdifference also applies within crownedgores. However, these “rollovers” shoulddesirably be 5% or less to minimize theeffect on vehicles inadvertently crossingthe gore area. It is recommended thatdetail grades for the above paved portion

of the gore area be provided to verify bothcross slopes and algebraic differences.The unpaved portion beyond the 22’ point(to the extent the clear zone from eachroadway overlaps) should be graded aslevel with the roadway as practical and beclear of major obstructions. See sketchbelow.


7. In order to identify the location of ramps at

interchanges, the following system oflettering ramps should be used on projectsinsofar as possible:

The northeasterly quadrant is designatedramp A. Ramps B, C, & D follow insequence in a clockwise direction.Interchange interior loops would similarlyfollow with clockwise designations E, F, G,& H.

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3.07.02 (continued)


C. Crossroads Over Freeways

Local or county roads over freeways shouldbe designed for stopping sight distance basedon the project design speed.

In interchange areas, the intersection sightdistance and clear vision areas at diamondramp terminals must be according to currentDepartment practice. See MDOT Sight Distance Guidelines, Section 3.03.02E and

the Geometric Design Guide GEO-370-Series.The driver's eye position, for a vehicle on aramp, is assumed to be between 14.5 feetminimum and 18 feet desirable from the edgeof the crossroad.

D. Ramp Radii

The speeds at which ramps may be driven, ifthey are free flowing, is determined primarilyby the sharpest curve on the ramp proper.Loop ramps, because of their designrestrictions, have the sharpest curvature, and

if possible the designer should not use aradius of less than 260 feet. For radii lessthan 260 feet, contact the Geometrics Unit ofthe Design Division.

E. Single Lane Ramp Widths

Single lane ramp widths are normally 16'-0".The total paved width including pavedshoulders should not exceed 28’. Widerpaved widths invite undesirable passing ofslow-moving vehicles or invite two-laneoperation.

Current ramp widths are shown in Chapter 6, Appendix 6-A.

3.07.03

Speed Change Lanes and Transitions

The change in vehicle speed betweenhighways and ramps is usually substantial,and provision should be made for accelerationand deceleration. Therefore, in order tominimize interference with through traffic onhighways, speed change lanes (decelerationand acceleration lanes) are added at turningroadways.

The Geometric Design Guides allow for eitherparallel or tapered deceleration lanes for exit

ramps. Parallel deceleration lanes should beused where the ramp exit is on a freewaycurve.




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3.07.04 (revised 2006)

Intersections

An intersection is defined as the general areawhere two or more highways join or cross,including the roadway and roadside facilitiesfor traffic movements within the area.

Intersections are an important part of ahighway facility because, to a great extent, theefficiency, safety, speed, cost of operation,and capacity of the facility depends on theirdesign. Although many of the intersectionsare located in urban areas, the principles

involved apply equally to design in rural areas.

The angle of intersection between theapproach road and the trunkline should not beless than 60° or more than 120°, withdesirable values between 75° and 105°.

The gradient of the intersecting roads shouldbe as flat as practical on those sections thatare to be used for storage of stopped vehicles.If possible, side roads should have a "landing"of no more than 3 percent grade. Even thoughstopping and accelerating distances for

passenger cars, on grades of 3 percent orless differ little from the distances on the level,larger vehicles need the flatter landing area.

Where two roadways intersect, crownmanipulation of both roadways can be used toimprove the drivability of both roadways. Inthis case, to insure proper drainage, detailgrades should be provided. See GeometricDesign Guide GEO-650-Series for allowableapproach road grades.

3.07.04 (continued)

Intersection sight distance should be provided

on all intersections legs. Clear vision cornersshould be provided when it is practical. SeeSection 5.24.

Center lanes for left turns or passing flaresmay be required at certain intersections. SeeGeometric Design Guide GEO-650-Series.

Ramp terminals should be according toGeometric Design Guide GEO-370-Series.

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3.08

3R, 4R AND OTHER PROJECTS

3.08.01 (revised 6-25-2012)

General

A. (3R) Resurfacing Restoration andRehabilitation

This work is defined in 23 CFR (Code ofFederal Regulations) as "work undertaken toextend the service life of an existing highwayand enhance highway safety. This includes

placement of additional surface materialand/or other work necessary to return anexisting roadway, including shoulders,bridges, the roadside and appurtenances to acondition of structural or functional adequacy.This work may include upgrading of geometricfeatures, such as widening, flattening curvesor improving sight distances." Examples ofthis type of work include:

1. Resurfacing, milling or profiling,concrete overlays and inlays (withoutremoving subbase).

2. Lane and/or shoulder widening (noincrease in number of through lanes).

3. Roadway base correction.

4. Minor alignment improvements.

5. Roadside safety improvements.

6. Signing, pavement marking and trafficsignals.

7. Intersection and railroad crossingupgrades.

8. Pavement joint repair.

9. Crush and shape and resurfacing.

10. Rubblize and resurface.

3.08.01A (continued)

11. Intermittent grade modifications (used tocorrect deficiencies in the verticalalignment by changing the paving profilefor short distances) that leave theexisting pavement in service for morethan 50% of the total project length.

12. Passing relief lanes.

See Chapter 12 of the Bridge Design Manualfor examples of “bridge” 3R work.

B. (4R) New Construction/

Reconstruction

Projects that are mainly comprised of thefollowing types of work are not considered 3R.

1. Complete removal and replacement ofpavement (including subbase).

2. Major alignment improvements.

3. Adding lanes for through traffic.

4. New roadways and /or bridges.

5. Complete bridge deck or superstructurereplacement.

6. Intermittent grade modifications (used tocorrect deficiencies in the verticalalignment by changing the paving profilefor short distances) that leave theexisting pavement in service for lessthan 50% of the total project length.

The above lists are not all inclusive, but areintended to give typical examples of 3R and4R work.

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3.08.01 (continued)

General

C. Combined 3R and 4R Work

If a project includes 3R and 4R work, theapplicable standards are governed by thestandards that correspond individually to eachwork type (3R or 4R). Identify the logicallimits of each work type on the projectinformation sheet to distinguish where 3Rguidelines and 4R standards are separatelyapplied. Work type overlap betweenseparation limits may cause a default to 4R

standards within the overlap.

When other work types are combined with 3Ror 4R projects, they are also governedseparately and identified as such on theproject information sheet. See Section3.08.01D.

D. Other Work Categories

Projects categorized by other work types suchas CPM, M-Funded Non-FreewayResurfacing, Signal Corridor and Signing

Corridor projects are governed by guidelinesthat differ from 3R and 4R Guidelines. Forinformation related to specific requirements forthese categories of work, use otherappropriate references. When other worktypes are packaged with a 3R or 4R project,the portion of the project that is outside the 3Ror 4R work limits is governed by theguidelines that pertain to the other work type.When describing the work type in the requestfor Plan Review Meeting, identify the logicallimits of work type separation so that theappropriate requirements are consideredwithin those limits. Work type overlap within

these separation limits may cause a default to3R or 4R requirements.

Note that the applicability of CPM minimumdesign requirements is contingent on theprogram eligibility of the roadway. Regardlessof funding source used to design andconstruct CPM work, CPM minimum designrequirements can only be applied to workdone on roadways that would otherwise beeligible for funding under the CPM program.

3.08.01 (continued)

E. Design Exceptions

The sections to follow include standards forgeometric design elements for the variousclassifications of roadways and work types.For specific controlling geometric designelements, a formal design exception must besubmitted and approved when the standardscan not be met. Design exceptions should beaddressed as early in the life of a design aspossible. Designers should strive to processdesign exceptions during the scoping process.

Along with the justification for not meeting

MDOT and/or AASHTO standards the designexception includes a crash analysis and theestimated total cost required to attain fullstandards compliance. See Section 14.11 f ordesign exception submittal procedures andrequired forms.

The controlling elements for which designexceptions are required include:

• Design Speed

• Lane Width

• Shoulder Width

• Bridge Width• Structural Capacity

• Horizontal Alignment

• Vertical Alignment

• Grade

• Stopping Sight Distance(Horizontal Sightline Offset (HSO) andK-value)

• Cross Slope

• Superelevation

• Vertical Clearance

• Horizontal Clearance (not including clear

zone, see definition of terms)• Ramps (See Section 3.11.03B)

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3.08.01E (continued)

General

When a bridge falls within a road project andno work is planned for the bridge, AASHTO“bridges to remain in place” criteria apply tothe bridges. See AASHTO publication,

A Policy on Design Standards-InterstateSystem, or A Pol icy on Geometric Designof Highways and Streets. If the bridge doesnot meet the criteria to “remain in place” theRoad Designer shall be responsible forsubmitting any necessary design exceptionsfor the bridge.

F. Safety Review / Crash Analysis

A safety review is required for all 3R and 4Rprojects. The Project Manager should contactthe TSC Traffic Engineer during scoping, sothat a safety review can be performedthroughout the project limits. On corridorprojects only one analysis that includesroadways and bridges is required. Thisreview should consist of an analysis ofavailable crash data to determine wheresafety enhancements are warranted. Safety

reviews more than 3 years old shall beupdated to verify the original safety review.

A site specific crash analysis is required as justification for any design exception. It is alsorequired in determining appropriate 3R designcriteria according to Section 3.09.02A and3.09.02B. Site specific crash analyses morethan 3 years old shall be updated to verify theoriginal crash analysis.

3.09

NON-FREEWAY RESURFACING,RESTORATION ANDREHABILITATION (3R) MINIMUMDESIGN GUIDELINES

3.09.01 (revised 1-6-99)

General The intent of the 3R guidelines is to extendthe useful life of existing roadways andenhance safety while incurring minimal

aesthetic and environmental disturbance andeconomic burden. Often, design guidelinesused for new and major reconstruction are notcost effective on 3R projects. Whereeconomically and physically practical, designguidelines should be according to AASHTOrequirements to insure the greatest trafficservice. The ultimate goal is to improveoperating conditions and provide highwaysthat are reasonably safe and fit for travel.

3R guidelines are divided into three categoriesthat are addressed in subsequent sections of

this chapter. These are NHS, Non-NHS and3R Safety Considerations. They apply strictlyto non-freeway applications. Guidelines forfreeway 3R and 4R type work are addressedseparately in Section 3.11.

3.09.02 (revised 11-21-2013)

3R Minimum Guidelines

Minimum guidelines for controlling designelements shall be according to the following:

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3.09.02 (continued)

A. Non-Freeway, NHS

Geometric Elements Non-Freeway, NHS 3R Minimum Guidelines Design Speed

(see Section 3.06) Posted Speed + 5 mph

Shoulder Width

Minimum shoulder widths applyfor:

Rural: Posted speeds greaterthan 45 mph.

Urban: Posted speeds greater

than 45 mph where sufficientright-of-way exists to includeshoulders.

At lower speeds, minimumshoulders are desirable.

Current ADTTwo-Way Inside

Shoulder OutsideShoulder

Two Lane

(and threelane when thecenter lane is

a left turnlane)

<750

750 - 5000

>5000 - 10,000

>10,000

3'-0" Gravel

6'-0" (3'-0" Paved)

8'-0" (3'-0" Paved)

8'-0" (7'-0" Paved)

Multi-LaneUndivided ≤ 10,000

> 10,000 6'-0" (3'-0" Paved)8'-0" (3'-0" Paved)

Multi-LaneDivided ≤ 10,000

> 10,000 3'-0" Paved3'-0" Paved 6'-0" (3'-0" Paved)

8'-0" (3'-0" Paved)

Lane Width

ADT Lane Width ≤750

>750

10'-0"

11'-0"

10'-0" lanes may be considered in urban areas for multi-laneun-divided (regardless of ADT) and multi-lane divided

(ADT < 10,000).

12'-0" lanes are desirable on the Priority Commercial Network (PCN). 12'-0" lanes are required on the National Network (also known as theNational Truck Network). Design exceptions to maintain existingnarrower lanes generally receive favorable consideration but a highburden of justification is placed on requests to reduce lane widths toless than 12’-0".

Bridge Width, StructuralCapacity & Horizontal

Clearances

Rural Urban Traveled way width plus 2'-0" each side.

Minimum Design Loading HS20. Curb to curb approach width.

Minimum Design Loading HS20. (See Bridge Design Manual Appendix 12.02 for other trunkline classifications)

Horizontal / Vertical Al ignment and Stopping

Sight Distance Existing alignment and stopping sight distance may be retained if the design speed ofthe existing curve is not more than 15 mph below the project design speed and thereis no crash concentration. Otherwise standards for new construction apply. Seecurrent AASHTO Green Book or MDOT Sight Distance Guidelines.

Grade Review crash data. Existing grade may be retained without crash concentration. Cross Slopes Traveled way 1.5% - 2%, Shoulder see Section 6.05.05

Superelevation Standard Plan R-107-Series or reduced maximum (6%) Straight Line SuperelevationChart using the project design speed.

Vertical Clearance See Section 3.12.

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3.09.02 (continued)

B. Non-Freeway, Non-NHS

Geometric Elements Non-Freeway, Non-NHS 3R Minimum Guidelines Design Speed Posted Speed Minimum

Shoulder Width

Minimum shoulder widths applyfor:

Rural: Posted speeds greater than45 mph.

Urban: Posted speeds greaterthan 45 mph where sufficient right-of-way exists to include shoulders.

At lower speeds, minimum

shoulders are desirable.

Current ADTTwo-Way Inside and Outside Shoulder Width ≤750

750 - 2000

> 2000

2'-0" (Gravel)

3'-0" (Paved)

6'-0" (3'-0" Paved) Multi-Lane

(Divided &Undivided)

Inside(Divided) Outside

(Both sides for un-divided) 3'-0" Paved 6'-0" (3'-0" Paved)

Lane Width

ADT Lane Width ≤750

>750 10'-0"

11'-0"

10'-0" lanes may be considered in urban areas for multi-laneun-divided (regardless of ADT) and multi-lane divided(ADT < 10,000).

12'-0" lanes are desirable on the Priority Commercial Network(PCN) and the National Network (also known as the NationalTruck Network). Existing narrower lanes may be retained

without design exceptions. Reduction of existing lane widths onthe National Network to less than 12-0" require a designexception request having a high burden of justification.

Bridge Width, StructuralCapacity & Horizontal

Clearances

(Existing Bridges toremain in place)

ADT(Design Year)

MinimumDesignLoading Usable Width

0 - 750 H15 Width of traveled way. 751 - 1500 HS15 Width of traveled way.

1501 - 2000 HS15 Width of traveled way plus 1' each side. 2001 - 4000 HS15 Width of traveled way plus 2' each side.

> 4000 HS15 Width of traveled way plus 3' each side. Horizontal / Vertical

Al ignment and StoppingSight Distance

Existing alignment and stopping sight distance may be retained if the design speedof the existing curve is not more than 15 mph (horizontal alignment) or 20 mph(vertical alignment) below the project design speed and there is no crashconcentration. Otherwise standards for new construction apply. . See current

AASHTO Green Book or MDOT Sight Distance Guidelines.

Grade Review crash data. Existing grade may be retained without crash concentration. Cross Slopes Traveled way 1.5% - 2%, Shoulder see Section 6.05.05

Superelevation Standard Plan R-107-Series or reduced maximum (6%) Straight Line SuperelevationChart using the project design speed.

Vertical Clearance See Section 3.12.





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3.09.02 (continued)

3R Minimum Guidelines

C. Design Exceptions

Non-freeway 3R minimum guidelines shouldbe followed on all non-freeway 3R projects,including Heritage Routes. When non-freeway3R guidelines are not met for any one or moreof controlling design elements (See Section3.08.01E.), a formal request for an exceptionshould be prepared.

When requesting exceptions to design

elements on Heritage Routes, it is important toaddress the fact that the requested exceptionis based on historic, economic, orenvironmental concerns for the preservationof the natural beauty or historic nature of thefacility.

D. Section Deleted

E. Vertical Curves

Without crash concentrations and/or othergeometric features such as intersections,

driveways, lane drops, and horizontal curveswarranting consideration, existing verticalcurves corresponding to a speed 0 to 15 mph(0 to 20 mph for Non-NHS) less than theproject design speed may be retained with asupporting site specific crash analysis.However, consideration should be given to re-grading vertical curves where economicallyand geometrically feasible. A designexception will not be required when anexisting vertical curve is improved to meet 3Rguidelines on 3R non-freeway projects, withverification that there is no crash

concentration attributed to the curve.However, in the presence of a crashconcentration, the curve shall be improved tomeet 4R guidelines. When entering sightdistance is restricted, an appropriate signwarning of the intersection may be installed,including advisory speed panels as needed.

3.09.02 (continued)

F. Horizontal Curves

Without crash concentrations that warrantrevision, existing horizontal curvescorresponding to a speed 0 to 15 mph lessthan the project design speed may be retainedwithout further documentation.

If the existing horizontal alignment is retained,the operation and safety should be improvedto the extent feasible through other elementssuch as superelevation modifications,removing adverse crown, and removal of sight

obstructions to improve stopping sightdistance. When the horizontal alignment doesnot meet the design speed, applicable trafficcontrol devices should be installed accordingto the Michigan Manual of Uniform TrafficControl Devices.

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3.09.03 (revised 9-20-2010)

3R Non-Freeway Safety Considerations

The following additional information serves asguidance for the review of existing andproposed roadside features. Policies onroadside features are not standards andtherefore do not require formal designexceptions. When deviations are necessary,a note should be written for the project file.This would not be subject to formal review orapproval, however, a note to the design fileshall provide the rationale for appropriatealternatives to these guidelines.

A. Signing

Consideration should be given to upgradingsign reflectivity, supports, and locations.

B. Evaluation of Guardrail and Bridge Rail

1. An onsite inspection of height, length, andoverall condition should be done todetermine guardrail upgrading needs

2. Existing Type A guardrail will be upgr adedto current standards (see Chapter 7) at alllocations, except as follows. Type Aguardrail which is in good condition maybe retained at cul-de-sacs, "T"intersections, and in front of the openingbetween twin overpassing structures.

3. Blunt ends and turned down endings shallbe upgraded to current standardterminals.

4. Unconnected guardrail to bridge railtransitions shall be connected or upgradedto current standards.

5. Existing bridge rail may remain in place ifit meets AASHTO static load requirementsand has an acceptable crash history.Otherwise, the bridge rail shall beupgraded or retrofitted with thrie beamguardrail. Note that new rail or completerail replacement shall meet currentstandards. See Bridge Design ManualSection 12.05.

6. By Federal mandate, existing BreakawayCable Terminals (BCT) must be removedon 3R projects on the National HighwaySystem (NHS). See Section 7.01.41B forupgrading guardrail terminal guidelines.

3.09.03 (continued)

C. Tree Removal

Tree removal will be selective and generally"fit" conditions within the existing right-of-wayand character of the road. The 2002

AASHTO Roadside Design Guide presentsideal clear zone distance criteria, however,these distances are not always practical inMichigan. Consequently, trees within theclear zone should be considered for removalsubject to the following criteria:

1. Crash Frequency

Where there is evidence of vehicle-treecrashes either from actual crash reports orscarring of the trees.

2. Outside of Horizontal Curves

Trees in target position on the outside ofcurves with a radius of 3000 feet or less.

3. Intersections and Railroad

Trees that are obstructing adequate sightdistance or are particularly vulnerable to beinghit.

4. Volunteer Tree Growth

Consider removal of volunteer trees within theoriginally intended tree line. Volunteer treesare those that have naturally occurred sinceoriginal construction of the road.

5. Maintain Consis tent Tree Line

Where a generally established tree line exists,consider removing trees that break thecontinuity of this line within the clear zone.

6. Clear Zone

See Section 7.01.11B for Treatment /consideration of obstacles inside thecalculated project clear zone. Review crashhistory for need for spot improvements.

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3.09.03 (continued)

D. Roadside Obstacles

Roadside improvements should be consideredto enhance safety. Improvements mayinclude removal, relocation, redesign, orshielding of obstacles such as culvertheadwalls, utility poles, and bridge supportsthat are within the clear zone as referenced inSection 3.09.03C.

A review of crash history will provide guidancefor possible treatments. However, treatmentof some obstacles, such as large culverts, can

add significantly, perhaps prohibitively, to thecost of a project. This means that in mostinstances only those obstacles that can becited as specifically related to crashes or canbe improved at low-cost should be included inthe project. Ends of culverts that are withinthe clear zone should be considered forblending into the slope. See MDOT DrainageManual, Section 5.3.5 and Table 5-1.

3.09.03D (continued)

Region Development or the requestor of the

project shall address these items in the scopeof the project to assure adequate funding forthe project. These considerations need to bemade at the scoping stage to allow the projectto progress smoothly through the designprocess.

E. Cross Section Elements

1. Crown Location

Existing pavement crown point location may

be retained on a project where the rate ofresurfacing is less than 4" in thickness.Otherwise, standard crown location should beused.

2. Side Slopes

Use the following chart for side slope rates:

3. Shoulder Cross Slopes

See Section 6.05.05.

3.09.04

Bridges

In most cases, bridge improvements willinclude upgrading approach guardrail,guardrail connections, and bridge rails tocurrent Department practices. See chapter 12 of the Bridge Design Manual.

Side Slopes

R e v i e w c

r a s h h i s t o r y f o r

i m p r o v e m e n t n e

e d s .

Current ADT Two-Way Foreslope

Two-Lane

≤ 750

> 750

1:3

1:4

Multi-Lane Undivided≤ 10,000

> 10,000

1:3

1:4

Multi-Lane Divided All 1:4

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3.09.05 (revised 11-28-2011)

Guidelines for Passing Relief Lanes

A. General

A passing relief lane, which is either a TruckClimbing Lane (TCL) or a Passing LaneSection (PLS), is intended to reducecongestion and improve operations alongtwo-way, two-lane, rural highways. Thecongestion (platoon forming) being addressedis the result of: (1) speed reduction caused byheavy vehicles on prolonged vertical grades(TCL), and/or (2) slow moving motorists incombination with high traffic volumes or

roadway alignment limiting passingopportunities (PLS). Platoons forming behindslow moving vehicles can be reduced ordispersed by increasing the speed or byincreasing the opportunities to pass them.The conditions that cause the forming ofplatoons also restrict the passing opportunitiesneeded to dissipate platoons, therebyincreasing congestion.

The construction of Passing Relief Lanes(PRL) is not intended to connect existingmultilane sections, but to provide a safe

opportunity to pass slower vehicles.

The Geometrics Unit in the Design Divisionshould be contacted to provide assistance inproject selection, location, and design basedon these guidelines.

B. Truck Climbing Lanes

The presence of heavy vehicles, as defined bythe 2000 Highway Capacity Manual (HCM),on two-way, two-lane highway grades cause aproblem because traffic is slowed and

platoons form simultaneously as passingrestrictions increase.

Warranting Criteria (TCL) (For Information Only)

Initially, design hour volumes (DHV) will beused in identifying candidate locations.Specific classification counts will be requested


when required for more comprehensive

analysis. FHWA requests that they beadvised on any Federal Aid Project in whichthe 30th high hour is not used as the DHV inwarranting a PRL. A combination of thefollowing should be considered in identifyingthe need for a TCL.

1. Upgrade traffic flow rate exceeds 200 vph

2. Upgrade truck flow rate exceeds 20 vph.

3. One of the following conditions exists:

a. Level-of-Service E or F exists on thegrade.

b. A reduction of two or morelevels-of-service is experienced whenmoving from the approach segment tothe grade.

c. A typical heavy truck experiences aspeed reduction of 10 mph or greateron the grade.

Location Consideration (TCL)

1. TCL’s should be:

a. On the upgrade side of “criticalgrades”.

b. Along sections relatively free fromcommercial or residential development(driveways) and away from majorintersections.

Design Consideration (TCL)

1. The TCL may normally be introduced onthe grade some distance beyond thebeginning of the upgrade because truckspeed will not be reduced enough tocreate intolerable conditions for followingdrivers until it has traveled a certaindistance up the grade.

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2. TCL’s should extend beyond the crest tothe point where a truck can attain a speedthat is within 10 mph of the speed of othertraffic and where decision sight distancewhen approaching the transition (taper)area is available.

3. The taper beginning a TCL should be atleast 500 feet long.

4. The taper length L (feet) is approximatelyW×S, where W is the shift in feet and S is

the posted speed in mph.

5. TCL’s should normally be 12'-0" wide.

6. TCL shoulders should be as wide as theshoulders on the adjacent two-lanesections but no less than 4'-0" (3'-0"paved). 4'-0" shoulders shall be limitedto areas where wider shoulders are notfeasible or environmental concernsprohibit wider shoulders.

C. Passing Lane Sections

Passing Lane Sections (PLS) along two-way,two-lane rural routes are often desirable evenin the absence of “critical grades” required forTCL’s. PLS’s are particularly advantageouswhere passing opportunities are limitedbecause of traffic volumes with a mix ofrecreational vehicles and/or roadwayalignment. It is preferable to have a four-lanecross section for a PLS, but that is not alwaysfeasible because of right-of-way orenvironmental concerns.

Warranting Criteria (PLS) (For Information Only)

Initially, design hour volumes (DHV) will beused in identifying candidate locations.Specific classification counts will be requestedwhen required for comprehensive analysis.

3.09.05C (continued)

FHWA requests that they be advised on any

Federal Aid Project in which the 30th highhour is not used as the DHV in warranting aPRL. A combination of the following shouldbe considered in identifying the need for aPLS.

1. Combined recreational and commercialvolumes exceed five percent of totaltraffic.

2. The level-of-service drops at least onelevel and is below Level B duringseasonal, high directional splits.

3. The two-way DHV does not exceed1200 vph. In situations where volumesexceed 1200 vph, other congestionmitigating measures should beinvestigated.

Location Cons iderations (PLS)

Desirably, PLS should be located in areas:

1. That can accommodate four lanes (PLSfor each direction of traffic) so that the

amount of three-lane sections isminimized.

2. With rolling terrain where vertical grades(even though not considered “criticalgrades”) are present to enhance:

a. Visibility to readily perceive both alane addition and lane drop.

b. Differential in speed between slow andfast traffic. This occurs on upgradelocations and produces increased

passing opportunities.

c. Slower vehicles regaining some speedbefore merging by continuing the PLSbeyond the crest of any grade.

3. Relatively free of commercial and/orresidential development (driveways) andaway from major intersections.

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3.09.05C (continued)


4. Where radius of the horizontal curve isgreater than or equal to 1900 feet.

5. With no restrictions in width resulting frombridges or major culverts, unless structurewidening is done in conjunction with PLSconstruction.

6. That are farther than 750 feet from arailroad crossing.

7. Where directional spacing of

approximately 5 miles can be maintained.

Design Considerations (PLS)

1. The beginning and ending transition(tapers) areas of a PLS should be locatedwhere adequate decision sight distance isavailable in advance.

2. The added lanes should continue over thecrest of any grade so that slower trafficcan regain some speed before merging.

3. The beginning or approach taper shouldbe at least 500 feet long.

4. The taper length L (feet) is approximatelyW×S, where W is the shift in feet and S isthe posted speed in mph.

5. The lane widths on any PLS shouldnormally be 12'-0" wide.

6. PLS shoulders should be as wide as theshoulders on adjacent two-lane sectionsbut no less than 4'-0" (3'-0" paved). 4'-0"shoulders shall be limited to areas wherewider shoulders are not feasible orenvironmental concerns prohibit widershoulders.

7. The desirable minimum length of any PLSis 1 mile with an upper limit of about 1½miles.

3.10

NON-FREEWAY RECONSTRUCTION /NEW CONSTRUCTION (4R)

3.10.01

General

“4R” projects are those that require completereconstruction, new alignment, or the additionof lanes for through traffic.

3.10.02

Design Criteria

These projects are to be designed to theGeometric Design Elements. See Appendix 3A.

3.10.03 (revised 2006)

Design Exceptions

Design Exceptions are required whenever thedesign criteria given above (Section 3.10.02)cannot be met for contr olling design elements

(See Section 3.08.01E.)

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3.11 (revised 2006)

FREEWAY RESURFACING,RESTORATION, REHABILITATION

AND RECONSTRUCTION / NEWCONSTRUCTION (3R/4R) DESIGNCRITERIA

3.11.01 (revised 1-14-2013)

General

The 3R/4R program applies to freeways,

which are defined as divided arterial highwayswith grade separated intersections and fullcontrol of access. Design criteria forInterstate freeways are established in the

AASHTO publication, A Policy on DesignStandards-Interstate System. Designcriteria for non interstate freeways areestablished in the AASHTO publication APolicy on Geometric Design of Highwaysand Streets.

Current freeway standards are shown in Appendix 3A. The standards used for designspeed, horizontal alignment, verticalalignment, and widths of median, traveled wayand shoulders for freeway 3R projects may bethe standards that were approved at the timeof original construction or reconstruction,whichever is most recent. See Section3.08.01C for information on combined 3R and4R work.

3R/4R freeway projects should be reviewed todetermine need for safety improvements suchas: alignment modifications, superelevation

modifications, sight distance improvements,lengthening ramps, widening shoulders,flattening slopes, increasing underclearances,upgrading guardrail and bridge railings,shielding of obstacles, and removing orrelocating obstacles to provide a traversableroadside. (Also see Section 3.08.01F.)

3.11.02 (revised 11-28-2011)

Freeway 3R/4R Checklis t

A. Sect ion Deleted

B. Geometrics and Signing

The Project Manager should also contact theGeometrics Unit in the Design Division andthe Region Traffic and Safety Engineer toidentify desirable enhancements prior torefining the project cost estimate. The DesignDivision – Traffic Sign Unit should be

consulted to identify and coordinate planpreparation for sign upgrading needs.

C. Section Deleted

D. Design Exceptions

Design Exceptions are required whenever thedesign criteria given in Section 3.11.01 cannotbe met for controlling design elements (SeeSection 3.08.01E.)

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3.11.03 (revised 4-23-2012)

Safety Considerations

A. Sect ion Deleted

B. Ramp Geometrics and Taper Lengths

When existing acceleration lanes,deceleration lanes and tapers are shorter thanthose shown in current MDOT guides, theyshould be lengthened to conform with thelatest Geometric Design Guides. If thesedistances cannot be achieved, designexceptions are required. Normally, it is morecost effective to use the parallel design for onand off ramps. The need for additional laneson the off ramp terminals should be analyzedfor capacity improvements. Radii should bechecked for adequacy. Gore areas should beflattened where desirable.

C. Vertical Curbs

Vertical curb should be entirely removed onfreeway mainlines, high speed turningroadways and collector distributor roads. Itshould also be removed on other ramps for aminimum distance of 200 feet from the

bifurcation or ramp nose.

3.11.03 (continued)

D. Sight Distances

Vertical and horizontal sight distances alongthe mainline and within the entire interchangearea, including ramp terminals, should bereviewed for conformance with current

AASHTO guides. See MDOT Sight DistanceGuidelines for more detailed discussion onsight distances.

E. Crown Location/Pavement Cross Slope

Where resurfacing is less than 4", the crown

point will be retained in its existing location,but the 2.0% cross slope should beestablished or maintained.

Where resurfacing is 4" or more, the crownpoint should be moved to meet currentstandards by shifting it to the left edge of theoutside lane. The 2.0% cross slope should beattained with the total yield kept close to440 lbs/syd for 4", 550 lbs/syd for 5", etc. byreducing thickness on the median lane.However, this concept of relocating thecrownline may not be feasible when the entire

pavement is sloped in one direction. Thedesirable roll-over or algebraic differencebetween the pavement and shoulder crossslopes is six percent or less. A designexception is required when an existing parabolic crown is retained. Also, see Section6.03.04B(1) “Crown and SuperelevationModification.”

F. Superelevation

Current Standard Plan R-107-Series shouldbe used to upgrade rural freeway projects,

when feasible. When it is not possible to usethe current Standard Plan R-107-Series, thestraight line method may be considered on acurve by curve basis as needed. SeeSuperelevation Using A Straight Line Methodin Section 3.04.03. A design exception isrequired if neither of these options can bemet.



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3.11.03 (continued)


G. Guardrail and Concrete Barrier

When designing barrier systems for ruralfreeways, use the 70 mph runout lengths fromthe runout chart in Section 7.01.19.

Piers and other obstacles near the center ofmedians, that are 70'-0" or less in width (edgeto edge), will always be shielded from bothsides, see Standard Plan R-56-Series.Obstacles in the median, near the edge of

pavements, will be shielded from the nearside. Shielding the far side will be determinedon a project-by-project basis.

When it is not possible to maintain currentguardrail offsets and still retain the 2'-0"distance from shoulder hinge line to the frontface of guardrail post, it is generally moredesirable to provide the additional offsetbetween the guardrail and pavement edgethan it is to reduce the offset in order tomaintain the 2'-0" distance. The shoulderwidth can be maximized by using 8'-0" posts

and relocating the guardrail to the shoulderhinge line. See 8'-0" post in Section7.01.41D.

When entire runs of guardrail are replaced,the types of rails for upgrading freeways arethe same as those specified in Section 7.01.12F for new freeways. The term"freeway" includes ramps. However, Type Tguardrail on ramps should be transitioned toType B when near a ramp terminal to avoid obstructing sight distance. See Section 7.01.41A.

3.11.03G (continued)

The need for median barrier will be reviewed

with the Geometric Design Unit.

The elimination of guardrail should beconsidered when economically feasible toflatten slopes, or where fixed objects can beremoved or relocated outside the clear zone.

H. Attenuation

Where physical conditions prohibit the use ofbarriers, but shielding is needed, attenuationdevices should be used. Contact the

Geometric Design Unit for attenuation design.

I. Shoulder Cross Slopes

See Section 6.05.05.

J. Section Deleted

Underclearance information in this sectionwas moved to Section 3.12.

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3.11.03 (continued)


K. Clear Zones & Fixed Objects

The current clear zone criteria specified inSection 7.01.11 should be used whenupgrading freeways. Obstacles within theselimits should be shielded or removed.Obstacles beyond these limits, but within therecovery area, should be reviewed by theGeometrics Unit in the Design Division.

L. Culvert End Treatments

The ends of culverts located within the clearzone on projects programmed for upgradingshall be according to MDOT DrainageManual, Section 5.3.5.

M. Bridges

See the Bridge Management Unit,Construction Field Services Division forFHWA conformance requirements.

3.12 (revised 1-14-2013)

UNDERCLEARANCES A. 4R Freeway

Roadway 4R projects on the Freeway Systemmust be designed to meet the current

AASHTO vertical clearance requirement of16'-0" (16'-3" is desired for future overlay ofthe road). Scoping of projects must include adetermination of the most effective means ofobtaining the vertical clearance standard. Acost/benefit analysis to determine how best toachieve the standard, either in full or with

incremental progress needs to be prepared.The analysis should include the alternatives ofobtaining all vertical clearances with the roadproject, a bridge project, or some combinationof road and bridge work to meet the clearancerequirements. In many cases it may not bepossible to achieve the complete verticalclearance with the proposed road project. Ifthe most efficient plan for meeting the verticalclearance requirement is incrementalprogress, a design exception will be required.The design exception should be submitted assoon as possible, preferably prior to the

submittal of the call for projects. This assuresthat design is not started on projects that maynot be approved. The following is theminimum information required to prepare avertical clearance analysis. This informationis also required if a design exception issubmitted.

Preliminary grades for the bridge andapproaches, the route under thestructure, and ramps if appropriate.

Location of existing structurefoundations related to the proposedgrade changes.

Impact evaluation on existing drainage.

Evaluation of any other deficientgeometric feature.

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3.12A (continued)

UNDERCLEARANCES

• Determination of ROW needs.

• Impacts on Environment.

• Cost estimates for alternatives to meetvertical clearances.

• Proposed time frame when theremainder of vertical clearance will beachieved (rough estimate)

• Accident analysis where appropriate.

• Soils (cut and fill information) andground water information.

• Impact on local businesses andresidences.

• User costs, constructability, maintainingtraffic scheme and maintenance cost.

B. 4R Arterials

On Roadway 4R projects on Arterial systems,where no work is scheduled for the bridges,the bridges are considered existing structuresand can be retained if they meet the 14'-6"vertical clearance standard, therefore nodesign exception is required. The existingclearance must be retained. It must not bereduced. Although not required, an evaluationshould be performed to determine how best toachieve the standard, either in full or withincremental progress. Obtaining incrementalprogress toward the vertical clearance

requirement with the road 4R project couldprevent other more costly construction withthe next major bridge rehabilitation orreplacement project.

C. 4R Collectors and Local Routes

Maintain existing vertical clearance and aminimum of 14'-6" (14'-9" is desired on 4Rprojects if possible.)

3.12 (continued)

D. 3R Freeway

Roadway 3R freeway projects must bedesigned to meet the current AASHTO verticalclearance requirement of 16'-0" (16'-3" isdesired for future overlay of the road). Adesign exception is required if the verticalclearance requirement is not met. The formatfor the design exception does not require adetailed evaluation but should include thebasis for the request and review of theaccident history and high load hits for thestructures in the immediate vicinity of the

structure.

E. 3R Arterials

On roadway 3R projects on Arterial systems,the bridges are considered existing structuresand can be retained if they meet the 14'-0"vertical clearance standard, therefore nodesign exception is required. The existingvertical underclearance must be retained.

Although not required, an evaluation shouldbe performed to determine how best toachieve the standard, either in full or with

incremental progress. Obtaining incrementalprogress toward the vertical clearancerequirement with the road 3R project couldprevent other more costly construction withthe next major bridge rehabilitation orreplacement project.

A design exception is required to maintain thevertical clearance below 14'-0". The likelihoodof obtaining design exceptions for reducingvertical clearance is extremely remote.

F. Preventive Maintenance

Project scope of work includes but is notlimited to road work consisting of thin HMAoverlays, pavement grinding, concrete jointrepair, slurry seal (shoulders only), and sealcoat (shoulders only). Maintain existingvertical clearance. No design exception isrequired.

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3.12 (continued)

UNDERCLEARANCES

G. Vertical Clearance Requi rement Table

The desired vertical bridge underclearance should be provided as indicated below. If the desiredunderclearance cannot be provided, then the minimum underclearance shall be met. Where it isconsidered not feasible to meet these minimums, a design exception shall be requested. See thevertical underclearance design exception matrix in this section and Section 12.02 of the BridgeDesign Manual. Requests to further reduce the underclearance of structures with existing verticalclearance less than indicated in the chart below should be made only in exceptional cases.

VERTICAL CLEARANCE REQUIREMENT TABLE

Route Classification

Under the Structure

All ConstructionNewConstruction

Road 4RConstruction

Bridge 4RConstruction

3R Construction

Desired Min Min Min Min

Freeways 16'-3" 16'-0" * 16'-0" * 16'-0" * 16'-0" *

NHS Arterials(Local & Trunkline) 16'-3" 16'-0" *

Maintain Existing14'-6" Min* 16'-0" * 14'-0" *

Non NHS Arterials(Local & Trunkline) 16'-3" 14'-6" *

Maintain Existing14'-6" Min*

Maintain Existing14'-6" Min* 14'-0" *

Collectors, Local Roads &

Special Routes(1)

14'-9" 14'-6" *Maintain Existing

14'-6" Min*Maintain Existing

14'-6" Min* 14'-0" *

* Minimum vertical clearance must be maintained over complete usable shoulder width.

Information on the NHS system can be obtained by contacting the Statewide Planning Section,Bureau of Transportation Planning or found on the MDOT Web site at:

http://www.michigan.gov/mdot-nfc

(1)Special Routes are in highly urbanized

areas (where little if any undeveloped landexist adjacent to the roadway) where analternate route of 16'-0" is available or hasbeen designated. Bridges located on SpecialRoutes in Highly Urbanized Areas can befound on the MDOT website at:http://mdotwas1.mdot.state.mi.us/public/design/englishbridgemanual/Exempt_Structures.pdf

Ramps and roadways connecting a SpecialRoute and a 16’-0” route require a verticalclearance minimum of 14’-6” (14’-9” desired).Ramps and roadways connecting two 16’-0”routes require a vertical clearance minimum of16’-0” (16’-3” desired).

Pedestrian bridges are to provide 1’-0” moreunderclearance than that required for avehicular bridge. For freeways (Interstate andnon Interstate), including Special RouteFreeways, the desired underclearance shall be17’-3” (17’-0” minimum).

A vertical clearance of 23’-0” is required forhighway grade separations over railroads.Clearance signs are to be present forstructures with underclearance 16’-0” or less(show dimensions 2” less than actual). Seehttp://mdotwas1.mdot.state.mi.us/public/tands/plans.cfm for additional information andguidelines.

For shared use paths (pedestrian and bicycle)the vertical clearance to obstructions,

including overhead fencing, shall be aminimum of 8’-6” (10’-0” desired). However,vertical clearance may need to be greater topermit passage of maintenance andemergency vehicles. In undercrossings andtunnels, 10’-0” is desirable for verticalclearance. See AASHTO’s Guide for theDevelopment of Bicycle Facilities.




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3.12 (continued)

UNDERCLEARANCES

H. Design Exception Requirements for Vertical Clearances

Design Exception RequirementsVertical Clearance

Type of Project DesignExceptionRequired

Coordinationwith

MTMCTEARequired

MDOT ApprovalRequired byEngineer of

Design Programs

FHWA Approval

New and 4R reconstruction work oninterstate greater than $1 million Yes Yes Yes Yes New and 4R reconstruction work onInterstate freeways less than$1 million.

Yes Yes Yes No

New and 4R reconstruction work onNon Interstate freeways greaterthan $1 million.

Yes No Yes Yes

New and 4R reconstruction work onNon Interstate freeways less than$1 million

Yes No Yes No

New and 4R reconstruction work onNHS routes other than freewaysgreater than $1 million.

Yes No Yes Yes

New and 4R reconstruction work onNHS routes other than freewaysless than $1 million.

Yes No Yes No

New and 4R reconstruction onNon-NHS Routes Yes No Yes No 3R work on Interstate System. Yes Yes Yes Only when

negotiatedoversight isassigned toFHWA on

NHSprojects >$5 million.

3R work on Non- Interstate System. Yes No Yes 3R work on Non-freeway Routes. Yes No Yes

Preventative Maintenance Work No No No No MTMCTEA - Military Traffic Management Command Transportation Engineering Agency

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3.12H (continued)

UNDERCLEARANCES

In addition to normal processing of designexceptions, all proposed design exceptionspertaining to vertical clearance on Interstateroutes including shoulders, and all ramps andcollector distributor roadways of Interstate toInterstate interchanges will be coordinatedwith the Surface Deployment and DistributionCommand Transportation Engineering Agency(SDDCTEA). The only Interstate routes theSDDCTEA is interested in are the routes thatrequire a 16'-0" vertical clearance. Theseroutes include all the Interstate systemincluding US-131 between I-196 and I-96(this roadway is technically I-296 but notsigned as such). In addition to the Interstateroute requirements listed above, US-23between Ohio state line and I-75 south ofFlint shall require coordination withSDDCTEA. This requirement does not applyto Special Routes (1).

MDOT (or its Consultant) is responsible forcoordinating exceptions on all projects

regardless of oversight responsibilities.MDOT will send a copy of all requests, andresponses, to the FHWA. Michigan InterstateVertical Clearance Exception Coordination,MDOT Form # 0333, is available from MDOTweb site.

3.12H (continued)

Requests for coordination shall be E-mailed orsent to:

Jason W. Cowin, P.E.Senior Engineer, Highway SystemsHighways for National Defense

ATTN: SDDCTEA709 Ward Drive, Building 1990Scott AFB, IL 62225 Telephone: 618-220-5229, Fax: 618-220-5125Email: [email protected]

MDOT (or its consultant) shall verify

SDDCTEA receipt of the request. If nocomments are received within ten workingdays, it may be assumed that the SDDCTEAdoes not have any concerns with theproposed design exception.

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n d b a r r i e r

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t r a f f i c e x c e e d s 2 5 0 D

D H V .

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D D H V .

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f t . ( 7 f t . p a v e d )

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n d r e c o n s t r u c t i o n ,

t h e m a i n l i n e o u t s i d e p a v e d s h o u l d e r i s e x t e n d e d w

i t h 1 f t . o f a g g r e g a t e

t o t h e s h o u l d e r h i n g e f o r s t a b i l i z a t i o n .

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s t a n d a r d w i d t h s ,

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r o v i d e t h e a d d i t i o n a l

f o o t o f a g g r e g a t e w h e n

f e a s i b l e .

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s u f f i c i e n t r i g h t - o f - w a y

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n o n f r e e w a y r u r a l

s h o u l d e r s . *

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c o n s t r u c t i o n a n d r e

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t h e

p a v e d s h o u l d e r i s e x t e n d e d w i t h 1 f t . o f a g g r e g a t e t o t h e s h o u l d e r h i n g e f o r s t a b i l i z a t i o n .

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t o r i g h t t u r n l a n e s .

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s h o u l d e r w i d t h s a p p l y f o r p o s t e d s p e e d s g r e a t e r t h a n 4 5 m p h .

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i n i m u m

s h o u l d e r s a r e

d e s i r a b l e .

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s e d , r e f e r t o

r e q u i r e m e n t s f o r r u r a l a r t e r i a l s .

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e h / d a y

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l d e r s a r e f e a s i b l e o n

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l

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l

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w a y

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t y p e

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r i a l )

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l

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l l e c

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N e w C o n s t r u c t i o n / R e c o n s t r u c t i o n

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n s i g h t d i s t a n c e c a l c u l a t i o n .

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o s e e S e c t i o n 6 . 0 5 . 0 5 )

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. 0 4 . 0 3 )

i o n

T h e a b

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i m u m r a t e i s 5 % f o r 6 0 m p h d e s i g n s p e e d .

N H S

N o n N H S

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a y

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N o n F

r e e w a y ( A r t e r i a l )

1 6 ’ - 0 ”

1 4 ’ - 6 ”

C o l l e c

t o r s & “ S p e c i a l R o u t e s "

1 4 ’ - 6 ” ( 1 f t . g r e a t e r t h a n M i c h i g a n l e g a l v e h i c l e h e i g h t . )

1 4 ’ - 6 ”

e

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d e s t r i a n b r i d g e s p r o v i d e 1 f t . a d d i t i o n a l c l e a r a n c e o v e r n o n - f r e e w a y a

n d 1 7 f t . m i n i m u m u n d e r c l e a r a n c e o v e r f r e e w a y s . A

v e r t i c a

l c l e a r a n c e o f 2 3 ’ - 0 ” i s r e q u i r e d f o r g r a d e s e p a r a t i o n s o v e r r a i l r o a d s .

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1 . 0

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3 - 0 4 . )

l / t h

S e e d e f i n i t i o n

o f t e r m s i n t h i s c h a p t e r . A l s o , s e e

B r i d g e D e s i g n G u i d e s ,

S e c t i o n 6




































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