2010 edition - dot.state.pa.us 652.pdf · guide rail or are longer posts required? this document...

PUB 652 (12-10)

Roadside SafetyPocket Guide

2010 Edition

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INTRODUCTION........................................................3

PART 1 – GUIDE RAIL BASICS ..............................4Barrier Warrants ....................................................4Clear Zone..............................................................5Design Options (In order of preference) ................7Types of Barrier ......................................................8Length of Need (LON) ..........................................12Length of Need Procedure ..................................13Length of Need for Opposing Traffic ....................14Length of Need (LON) Field Check ......................15Additional Design Considerations ........................15Design Deflection Distance ..................................15Height Measurement ............................................16Guide Rail Flare Rates ........................................17Barrier Placement on Slopes................................18Guidelines for Barrier on Slopes ..........................19Guide Rail and Curb ............................................19Guide Rail and Trees............................................20Guide Rail Transitions ..........................................21Connections to Bridge Barriers ............................22

PART 2 – SPECIAL CASES....................................23Missing Post(s)/Nested Panels ............................23Guide Rail at Intersections and Driveways ..........28

PART 3 – END TERMINALS ..................................29End Terminals ......................................................29Types of End Treatments ....................................30Turndown End Terminals......................................34Terminal Grading Details ......................................34

PART 4 - MAINTENANCE ......................................37Longitudinal Barrier Damage................................38Terminal Damage ................................................38Repair/Upgrade/Remove......................................38

GUIDE RAIL REFERENCES ..................................40

Table of Contents

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Guide rail systems are designed and installed for oneprimary reason: to reduce the severity of a crash bypreventing a motorist from reaching a morehazardous fixed object or terrain feature. The purposeof this document is to summarize importantinformation contained in PennDOT's Publication 13M,Design Manual Part 2 (DM-2); Publication 72M,Roadway Construction Standards; and Publication 23,Maintenance Manual that can be used in the field toensure that all barrier installations are built andmaintained to current standards and can be expectedto perform acceptably when hit.

Questions We Must Ask Ourselves

When in the field we need to ask ourselves thefollowing questions:

1. Is the guide rail system more hazardous thanwhat we are shielding?

2. Is this existing guide rail installation warranted?3. If we terminate the guide rail here – is there a

possibility of a motorist hitting the hazard?4. If we extend the guide rail – is there another

obstruction we could be shielding? 5. Are there any obstructions that are in the guide

rail system’s deflection zone?6. Are we terminating the guide rail within 200 feet

of the start of another guide rail string?7. Are we terminating the guide rail string within 200

feet of a cut slope?8. Does the slope need any regrading?9. Has the guide rail height been reset after an

overlay?10. Are we using the best end treatment for the field

condition?11. Are we considering guide rail in sensitive areas

such as school playgrounds and reservoirs?12. Is there adequate backup behind strong post

guide rail or are longer posts required?

This document provides the information needed toanswer these and other questions pertaining tooptimal design, installation, and maintenanceconsiderations for guide rail systems.

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PUB 652 2010 Edition

Introduction

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Barrier Warrants• Are pre-determined situations or conditions where

a traffic barrier is normally considered. Refer to theTables on page 6 for embankment and fixed objectwarrants.

• These warrants should be considered asguidelines for determining the need for a barrierrather than absolute criteria.

• They are not a substitute for engineeringjudgment.

Establishing Barrier Warrants• Barrier warrants are based on the premise that a

traffic barrier should be installed only if it reducesthe severity of potential crashes.

• There are instances where it is not immediatelyobvious whether the barrier or the unshieldedcondition presents the greater danger to amotorist.

• In such instances, warrants may be established byusing a benefit/cost analysis whereby factors suchas design speed, roadway alignment, and trafficvolumes can be evaluated in relation to barrierneed.

• Costs associated with the barrier (installation,maintenance, and crash-related costs) arecompared to crash costs associated with theunshielded condition.

• This procedure is typically used to evaluate threeoptions: 1. Remove or reduce the condition so that it no

longer requires shielding or2. Install an appropriate barrier or3. Leave the condition unshielded

Considerations• Consider eliminating short lengths of guide rail

since these sections are often more undesirablethan no barrier at all.

• Avoid short gaps between guide rail installationsby making guide rail continuous where the pointsof need are determined to be about 200 feet apartor less.

• Consider keeping the slope clear of fixed objectswhen guide rail is not required due to the height ofthe slope.

• Consider guide rail in sensitive areas such asschool playgrounds or reservoirs even when they are outside the clear zone, which isdiscussed next.

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Part 1 - Guide Rail Basics

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Clear ZoneThe term “clear zone” is used to designate an areabordering the roadway, starting at the edge of thetraveled lane, which is available for safe use by errantvehicles. Safe use generally means the slope is flatenough and free of fixed object hazards so a motoristleaving the road is able to stop and return to theroadway safely. The clear zone distances shownbelow represent minimum recommended distancesand are based on limited data. The best answer to thequestion “How wide should the clear zone be ?” is “Aswide as practical in each situation – but at least aswide as the tabulated distances”.

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Minimum Clear Zone Widths (in feet)

**Since recovery is less likely on the unshielded, traversable 1V:3H slopes,consider removal of fixed objects present beyond the toe of these slopes.Determination of the width of the recovery area provided, if any, at the toe ofslope should take into consideration right-of-way availability, environmentalconcerns, economic factors, safety needs, and crash histories. Also, the distancebetween the edge of the through traveled lane and the beginning of the 1V:3Hslope should influence the recovery area provided at the toe of the slope.

Design DesignSpeed Average(mph) Daily Traffic

Foreslope Backslope

1V:6H or

Flatter

1V:5H to

1V:4H1V:3H 1V:3H

1V:5HTo

1V:4H

1V:6H or

Flatter

40 mphor less

45 – 50mph

55 mph

60 mph

65 – 70mph

Under 750 7 7 ** 7 7 7

750 – 1500 10 12 ** 10 10 10

1500 – 6000 12 14 ** 12 12 12

Over 6000 14 16 ** 14 14 14

Under 750 10 12 ** 8 8 10

750 – 1500 14 16 ** 10 12 14

1500 – 6000 16 20 ** 12 14 16

Over 6000 20 24 ** 14 18 20

Under 750 12 14 ** 8 10 10

750 – 1500 16 20 ** 10 14 16

1500 – 6000 20 24 ** 14 16 20

Over 6000 22 26 ** 16 20 22

Under 750 16 20 ** 10 12 14

750 – 1500 20 26 ** 12 16 20

1500 – 6000 26 30 ** 14 18 24

Over 6000 30 30 ** 20 24 26

Under 750 18 20 ** 10 14 14

750 – 1500 24 28 ** 12 18 20

1500 – 6000 28 30 ** 16 22 26

Over 6000 30 30 ** 22 26 28

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Barrier Requirements for Embankment Heights

Guide Rail Requirements for FixedObjects Within the Clear Zone

*The designer shall exercise sound engineering judgment and considerprotection in some special cases where such obstructions are likely to be hit dueto geometric roadway conditions (outside of a curve, steep grade at beginning ofa curve, etc.). Shielding should also be considered in sensitive areas such asschool playgrounds and reservoirs. **A judgment decision based on relativesmoothness of wall and anticipated maximum angle of impact.

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Design Options (In order of preference)

• Remove the obstruction.• Redesign the obstruction so it can be traversed

safely.• Relocate the obstruction to a point where it is less

likely to be struck.• Reduce impact severity by using an appropriate

breakaway device or impact attenuator.• Shield the obstruction with a longitudinal traffic

barrier if it cannot be eliminated, relocated orredesigned.

• Delineate the obstruction if the above alternativesare not appropriate.

REMEMBER: Guide rail can also be a hazard andshould only be used where the results of leaving theroadway and overturning or striking a fixed objectwould be more severe than the consequence ofstriking the barrier.

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Types of BarrierFlexible Systems: Weak Post W-Beam Guide RailTypes:

• 2-W (normal post spacing)

• 2-WC (close post spacing)

• 2-WCC (very close post spacing)

Semi-Rigid Systems: Strong-Steel Post W-BeamGuide Rail with Wood or Plastic Block Types:

• 2-S (normal post spacing)

• 2-SC (close post spacing)

• 2-SCC (very close post spacing)

Rigid Systems: Permanent Concrete Barrier

Weak Post Guide Rail (2-W, 2-WC, and 2-WCC)should be used if the minimum unobstructed distancebehind the rail is available. See Deflection Table onpage 15.

Weak Post Systems should not be used if the fillslope is steeper than 1V:1.5H. Weak post guide railshall not be used around radii at intersections where itcan be hit at severe impact angles.

Strong Post Guide Rail (2-S, 2-SC, 2-SCC) shouldbe used when the minimum unobstructed distancebehind the rail is not adequate to permit the use of aweak post system. See Deflection Table on page 15.

Mixing of strong post and weak post systems inthe same run of guide rail shall be used only when theproper transition treatment between systems can beprovided, as shown on the Standard Drawings.Frequent transitions between strong post and weakpost systems should be avoided. Refer to page 21 formore information.

High-Tension Cable Median Barrier is installed witha significantly greater tension in the cables thangeneric three-cable systems. The deflection of thesesystems depends on the type of system and the postspacing. The high-tension systems also result in lessdamage to the barrier and usually the cables remainat the proper height after an impact that damagesseveral posts. The posts can be installed in concretesleeves in the ground to facilitate removal andreplacement. The table on page 11 presentsdesign/location guidelines for high-tension cablebarrier systems.

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High Tension Cable Median BarrierCurrently there are only proprietary systems of cablebarriers which are to be used in median applications.

Examples follow below.

Brifen Wire Rope Safety Fence (WRSF) by Brifen USA

Top Rope Height: 36 ½”

Deflection Distance astested under NCHRPReport 350:

Small car: 4ʼ- 5 1/8” for10ʼ- 6” post spacing.

Single-unit truck:7ʼ- 3” for 10ʼ- 6” postspacing.

Pick-up truck: 7ʼ-10 4/8”for 10ʼ- 6” post spacing.

Posts are set in tubular steel sockets contained incylindrical concrete footings. Lower 3 cables weavebetween posts.

Gibraltar

Top Rope Height: 39”

Deflection Distancetested under NCHRPReport 350:

Small car: 2ʼ- 6” for 15ʼpost spacing (TL-3).

Single-unit truck: 7ʼ for14ʼ post spacing (TL-4).

Pick-up truck: 8ʼ- 7 2/8” for 15ʼ post spacing (TL-3).

Fourth cable is anchored. Taper the 25-inch highcable down to the bottom (20-inch) cable between thefirst line post and the last terminal post and connectthe two cables with a series of four clamps spaced 4.5inches apart along the 20-inch high bottom cable.(NOTE: 3 cable design is shown).

Foundation Type: Line post can be driven or socketed. Posts are set on alternate sides of cables.

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Safence by Gregory Highway Products

Top Rope Height: 28 3/8”

Deflection Distance astested under NCHRPReport 350:

Single-unit truck: 7ʼ- 2 5/8”for 13ʼ- 2 3/8” post spacing.

Pick-up truck: 6ʼ-10 5/8”for 13 ̓-2 3/8” post spacing.

Fourth cable is anchored with its own

connection to the concrete terminal block.

Foundation Type: Socketed

CASS by Trinity


Deflection Distance as testedunder NCHRP Report 350 forCASS TL-3:

Single-unit truck: 7ʼ- 2 6/8” for 20ʼpost spacing.

Pick-up truck: 7ʼ- 8 7/8” for 20ʼpost spacing.

A four cable design adds afourth cable midway betweenthe bottom and middle cablesof the original TL-4 CASS.

Foundation Type: The CASSsystem posts can be driven, installed in a drivensleeve, installed in a sleeve in a concrete footing(poured or pre-cast), or mounted to a concrete sur-face.

Nu-Cable by Nucor Marion Steel


Deflection Distance as testedunder NCHRP Report 350:

Small-car: 4ʼ - 7 1/8” for 20ʼ postspacing.

Single-unit truck: 7ʼ - 6 1/8” for 20ʼpost spacing.

Pick-up truck: 9ʼ -6 1/8”

Foundation Type: Socketed

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Design/Location Table for High TensionCable Barrier Systems

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NOTE: The Highway Quality Assurance Division of the Bureau of Project Deliverywill provide assistance in evaluating design considerations for these systems andin addressing concerns raised by using these systems.See DM-2 Table 12.9

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Length of Need (LON) Is defined as the length ofbarrier needed in advance (upstream) of a fixedobject hazard or a non-traversable terrain feature toprevent a vehicle that has left the roadway fromreaching the shielded feature. It is determined byselecting the appropriate variables and using theformula on page 13 to calculate the LON (the “X”value) shown in the diagram below.

Approach Barrier Layout

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X = Distance from the obstruction to end of barrier need.

Y = Distance from edge of through traveled way to end of barrier need.

LA = Distance from edge of through traveled way to lateral extent of obstruction.

L1 = Tangent length of barrier upstream from obstruction.

L2 = Distance from edge of through traveled way to barrier.

L3 = Distance from edge of through traveled way to obstruction.

LC = Distance from edge of through traveled way to outside edge of the clear zone.

LR = The theoretical Runout Length needed for a vehicle leaving the roadway to stop.

a : b = Flare Rate.

See DM-2 Figure 12.3 and RC-54M, Sheet 3.

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Length of Need Procedure:1. Choose an appropriate LA as it is a critical part of

the design process. This distance should includeall features or hazards that need to be shielded,up to the design clear zone at each site.

2. Select a Runout Length (LR) from the table below.

3. The designer selects tangent length, (L1). If asemi rigid barrier is connected to a rigid barrier,the tangent length should be at least as long asthe transition section. See page 8 for types ofbarrier.

4. If the barrier is flared away from the roadway, themaximum recommended flare rate shown on page17 should not be exceeded.

5. Calculate the Length of Need (X) from thefollowing equation and round the calculated valueup to the nearest 12.5-foot or 25-foot rail segment:

6. For parallel installations i.e. no flare rate, theprevious equation becomes:

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Runout Lengths

See DM-2 Table 12.8

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Length of Need for Opposing Traffic

• X is determined using the same equation.

• All lateral dimensions are measured from the

centerline for a two-lane roadway. See the layoutat the bottom of this page.

• Three ranges of clear zone width, LC, that

deserve special attention:

1. If the barrier is beyond the appropriate clear zone for opposite direction traffic, no additional barrier and no crashworthy end treatment is required. (NOTE: an appropriate barrier anchor remains necessary to ensure proper containment and redirection for near-side impacts).

2. If the barrier is within the appropriate clear zone but the area of concern is beyond it, no additional barrier is required; however a crashworthy end treatment should be used.

3. If the area of concern extends well beyond the appropriate clear zone (e.g., a river), the designer may choose to shield only that portion which lies within the clear zone, by setting LA equal to LC.

Approach Barrier Layout for Opposing Traffic

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See DM-2 Figure 12.4 and RC-54M, Sheet 3

CLEAR ZONE LINE FOR OPPOSING TRAFFIC

AREA OF CONCERN

END OFBARRIER

OPPOSING TRAFFIC

PROPERUSE

ENDTREATMENT

(OBSTRUCTION)

ADJACENT TRAFFIC

EDGE OF THROUGH TRAVELED WAY

NEED

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Length of Need (LON) Field Check:A straightforward method to verify correct LON in thefield is to stand on the roadway edge directly oppositethe shielded feature, and then pace off theappropriate runout length from the Table on page 13.At that point, turn and look at the shielded area. If theproposed (or actual) guide rail installation crossesthat line of sight, then the area is adequatelycovered.(NOTE: if the terrain makes it impossible fora vehicle to reach the hazard from that point, theinstallation may be too long. On the other hand, if theintervening terrain is also hazardous or if there areother significant obstacles in the immediate vicinity, itmay be desirable to extend the barrier to shield all ofthe dangerous conditions.)

Additional Design Considerations:Although it is critical that the correct LON be installed,there are several other placement considerationsessential to good barrier performance. These includeminimum unobstructed distances behind each type ofbarrier, barrier height, guide rail flare rates, and thelocation of barrier on slopes and behind curbs. Thesefactors are discussed in the next sections.

Design Deflection Distance is based onthe results of 62-mph impacts into the barrier at a 25-degree impact angle by the NCHRP Report 350 orMASH pickup truck. In the field, actual deflections canbe much greater (or less) depending on actual impactconditions.

Deflection Table(Minimum Unobstructed Distance)*

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Height Measurement: The minimum height ofStrong-Steel Post W-Beam Guide (2-S) is 27 ¾”,measured as shown below or from the gutter linewhen set above a curb.

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Guide Rail Flare Rates• A roadside barrier is considered flared when it is

not parallel to the edge of traveled way.

• The flare is normally used to locate the barrierterminal farther from the roadway and/or to reducethe total length of barrier needed.

• Disadvantages are it increases the angle of impactwhen struck and may require extensive sitegrading to ensure a flat approach.

Flare Rates for Barrier:

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Flare Rates for Barrier

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Barrier Placement on Slopes: Barrier,regardless of type, performs best when an impactingvehicle is stable when contact is first made. Sincevehicles running off the road at high speeds tend tobecome airborne and are likely to override barrierplaced on a slope, the following guidelines should befollowed:

1. On 1V:6H Slope

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2. For Optimum Performance

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Guidelines for Barrier on Slopes

• Do not place guide rail on slopes steeper than1V:6H.

• W-beam systems can be placed anywhere on1V:10H or flatter slopes.

• When the slopes are between 1V:10H and 1V:6H,the face of the barrier must not be between 2 to12 feet beyond the grade hinge point.

• Strong post systems need 2 feet of soil supportbehind the rail for support. When 2 feet is notobtainable, strong posts that are a minimum of 1foot longer shall be provided.

• Cable barrier can be placed anywhere on a 1V:6Hslope or flatter. Most proprietary systems can beplaced on 1V:4H slopes, but manufacturers’recommendations must be followed.

Guide Rail and Curb

Curbs do not have a significant redirection capabilityand can have the same type effect on vehicletrajectory as slopes, i.e., wheel impact with a curb cancause a vehicle to vault over a barrier placed aboveor beyond it. The following guidelines apply:

• Guide Rail should not be used with curbinstallation on high speed (45 mph and higher),rural roads.

• When guide rail/curb installation is unavoidable,keep curb height to a maximum of 4 inches anduse strong post guide rail.

• If the curb exceeds 4 inches, follow theseguidelines:

1. Type 2-S or 2-SC guide rail should be used.

2. Stiffen the guide rail

o Add a rubrail or

o Double nest the rail or

o Bolt a W-beam to back of the posts

3. Curb must be flush with, or slightly behind, with the face of guide rail.

4. The guide rail height is measured from the gutter line to the top of rail when the guide rail is placed in front of or at the face of the curb.

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Guide Rail and Trees• Generally guide rail should not be used to shield a

line of utility poles or trees.• Where guide rail is used in front of poles or trees

due to other obstructions use the Deflection Tableon page 15.

• Consider removing trees where they are anobstruction and in locations where they are likelyto be hit.

• Use crash history at similar sites, scars indicatingprevious crashes or field views to determineremovable trees.

• Tree removal is usually a preferred option but anassessment regarding its expense andeffectiveness should be considered.

• Roadways through wooded areas with heavynighttime traffic volumes, frequent fog and narrowlanes should be well delineated.

• Pavement markings and post mounted delineatorsare among the most effective and least costlyimprovements that can be made to a roadway.

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Guide Rail Transitions

If a transition is not used or is not properly designed,a vehicle may deflect the more flexible system andpocket or snag on the stiffer section.

• When guide rail approaches an obstacle thatrequires a stiffer, stronger system, introduce 25-foot increments of stronger guide rail systems fora gradual increase in strength.

• Frequent transitions between strong post andweak post systems should be avoided.

For example, transition from Weak Post Guide Rail toan obstruction with 1 foot of deflection distance asfollows:

• Type 2-W (12’-6” post spacing) to

• 25 feet of Type 2-WC (6’-3” post spacing) to

• 25 feet of Type 2-WCC (3’-1 ½” post spacing) to

• 25 feet of Type 2-S (6’-3” post spacing) to

• 25 feet of Type 2-SC (3’-1 ½” post spacing) to

• Type 2-SCC (1’-6 ¾” post spacing) in front of the obstruction

NOTE: The number and types of transitions depend uponthe obstruction’s deflection distance.

See RC-50M and RC-54M for more information

This installation transitions from a WeakPost System to a Strong Post System.Note the height transitionfrom W to S

Type 2-SCCType 2-S

Type 2-WCC

Type 2-WC

Type 2-W

Type 2-SC

Guiderail Transition-2-W to 2-SC

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Connections to Bridge Barriers Since there are numerous bridge barrier designs currently in place on Pennsylvania highways, the attachment details shown in the RC Standards fornew construction and reconstruction will not alwaysbe directly applicable for every project. However,crashworthy designs can be developed if three concerns are met: an adequate transition between the bridge end and the approach guide rail, an adequate attachment to the bridge barrier itself, andthe elimination of any potential snag points at thebridge end.

• A transition is simply a gradual stiffening of the approach guide rail at the bridge end so the railcannot deflect enough to result in a vehicle “pocketing” when it reaches the rigid bridge barrier. Acceptable transition designs for somespecific existing bridge barriers are shown in DM-2, Chapter 12, Appendix A.

• A structurally adequate attachment of the guiderail to the bridge barrier is shown on the transitiondetails as well. This detail is needed to prevent theapproach railing from pulling free from the bridgebarrier. In some cases, the existing bridge barrieritself may not be structurally adequate to supportsuch a connection. For many such structures, extending the guide rail across the structure eliminates the need for a structural connection atthe bridge end and may increase the capacity ofthe bridge barrier itself.

• Finally, if the bridge barrier is significantly higherthan the approach railing, a truck or SUV impacting the approach railing could lean over therailing far enough to snag on the end of the bridgebarrier, or if no rubrail is used, a vehicleʼs tirecould fold under the guide rail and snag on thebottom edge of the bridge parapet.

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Missing Post(s)/Nesting Panels

These designs can be used when site conditions donot permit standard spacing of guide rail posts. Typi-cal situations are locations where barrier must be con-tinuous over a low-fill culvert, span a buried utility line,or where isolated rock prevents driving a post. Tocompensate for the missing posts, the following modi-fications need to be made to the barrier design:

Key to remember:

• When skipping a type 2-S Guide Rail Post, nest

panels to maintain the guide rail strength.

• Provide a minimum of 200 feet of strong postguide rail between nested runs.

See RC-52M, Sheets 6, 7 and 8 for more information

Typical Nested Panel

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Part 2 - Special Cases

NOTE: Two sections of W-Beam rail element, one setinside the other. Splice connection shown.

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Case 1 - 3 Nested Panels

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NOTE: A minimum unobstructed distance of 3’-0” behindthe rear face of guide rail post must be clear of hazardswith the elimination of one post.

Case 2 – 2 Nested Panels

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Case 1 – Splice Locations

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NOTE: A minimum unobstructed distance of 3’-6” behindthe rear face of guide rail post must be clear of hazardswith the elimination of two posts.


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nNOTE: A minimum unobstructed distance of 5’-0” behind the rear face of guide rail post must be clear ofhazards with the elimination of three posts. The three posts on either side of the clear span are breakawaytimber posts with two offset blocks.


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NOTE: A minimum unobstructed distance of 5’-0” behind the rear face of guide rail post must be clear of hazards with theelimination of three posts. The three posts on either side of the clear span are breakaway timber posts with two offset blocks.


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Guide Rail at Intersections and DrivewaysGuide rail installations at these and similar typelocations present a challenge to the designer, butthere are two major concerns that should be met. Thefirst is to be sure the railing along the main roadway isin tension so impacting vehicles will be contained andredirected away from the shielded hazard. One way toaccomplish this to be sure the railing parallel to themain roadway is long enough to develop tension forimpacts downstream from the curved portion ofbarrier. The second concern is to prevent vehiclesimpacting the curved portion of the railing fromvaulting over it. Some DOTs do this by usingweakened posts without blockouts in this area so theposts break immediately on impact, allowing the railelement to wrap around the front of the impactingvehicle and slow it gradually.

Intersections:• Type 2-S Guide Rail around radius.

• Approved end terminal on intersecting side road. Iftraffic on the minor road is controlled by a STOPsign, a turn down terminal may be appropriate.

Driveways:• Type 2-S Guide Rail around radius.

• Terminate the guide rail outside the clear zone ifpossible with a proper end treatment or a terminalsection or turn down may be used on thedriveway.

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End TerminalsPrevent errant vehicles from impacting fixed objectsby either gradually decelerating the vehicle to a stopwhen hit head-on, or by redirecting it away from theshielded object or terrain feature when the barrier isstruck on the traffic face near the terminal.

• National Cooperative Highway Research Program (NCHRP) guide rail requirements

• Acceptable End Terminals

o Type I - Anchored in Backslope Terminal

o Type II - Energy Absorbing Terminals

o Type III - Non-Energy Absorbing Terminals

o Type IV - Gating Systems for Two-Way Traffic

o Type V - Non-Gating Systems for Two-Way Traffic

o Type VI - Gating, Non-Redirective Crash Cushions

o Turndown End Terminals

Classifications:

Energy Absorbing terminals stop vehicles safely inrelatively short distances in end-on impacts (usually50 feet or less depending on type of terminal).

Non-Energy Absorbing systems will allow anunbraked vehicle to travel 150 feet or more behindand parallel to guide rail installation or along the top ofthe barrier when struck head-on at high speeds.

Flared: Have a 4-foot parabolic (curved) offset at the approach end, but require a larger platform to sit upon.

Tangent: installed parallel to the shoulder with a 2-foot offset over the first 50 feet of length.

NOTE:

• At the trailing end of guide rail, a distance of 50feet beyond the end treatment is to be kept clearof all roadside obstructions.

• This "downstream clear zone" is intended tominimize the likelihood that a vehicle may bedirected into an obstruction by the barrier

Part 3 - End Terminals

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• On two lane highways with two way traffic, provide end treatment on both the approach and trailing ends of the guide rail

• On four-lane divided highways, use end treatments on the approach ends only

• All ends of weak post guide rail must have appropriate transition to Type 2-S Guide Rail before installing Types II, III or IV end treatments.

Types of End Treatments

NOTE: Devices listed are current at the time of printing

Type I – Anchored in Backslope Terminal

• The most desirable method to terminate guiderail is to bury the end in a back slope that is aminimum of 1V:3H, but preferably steeper.

• Must maintain full height of guide rail in relationto roadway. If the distance from the bottom of therail to the ground exceeds 18 inches, a rubrailmust be added.

• Should also be used when the barrier system’sLON would normally end downstream of a cutslope if the cut slope is within 200 feet and thereis not a large runout area (200 ft x 50 ft)available.

See RC-54M, Sheet 5

Note that the height of theguide rail is held constant

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Type II – Energy Absorbing Terminals

• Used for single runs of strong post*

• Redirection begins beyond the third post

• See RC-54 for grading details

NCHRP 350 Approved Type II Terminals

• Flared Energy Absorbing Terminal (FLEAT-350)

• Extruder Terminal (ET-2000)

• Sequentially Kinking Terminal (SKT-350)

• Box Beam Bursting Energy Absorbing TerminalSingle-Sided Crash Cushion (BEAT-SSCC)

Type III – Non-Energy Absorbing Terminals

• Used for single runs of strong post*

• Redirection begins beyond the third post

• See RC-54 for grading details

NCHRP 350 Approved Type III Terminals

• Slotted Rail Terminal (SRT-350)

• Modified Eccentric Loader Terminal (MELT)

Can only be used at locations where speedlimit is 45 mph or below.

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Type IV – Gating Systems for Two-Way Traffic

• Used for double-faced strong post* guide rail,and concrete median barrier

• Minimum width of 10 feet needed

• Redirection varies for each device

• Can be permanent or temporary

*Must have appropriate transition to Type 2-S GuideRail before installing Types II, III or IV endtreatments.

NCHRP 350 Approved Type IV Terminals

• Crash-Cushion Attenuating Terminal (CAT-350)

• Brakemaster 350

• Advanced Dynamic Impact Extension Module(ADIEM)

• Flared Energy Absorbing Terminal – MedianTerminal (FLEAT-MT)

Type V – Non-Gating System for Two-Way Traffic

• Used for concrete median barrier, double-facedstrong post guide rail, and other obstructions

• Used in narrow or wide roadway medians

• Redirection begins at approach end

• Can be permanent or temporary

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NCHRP 350 Approved Type V Terminals

• QuadGuard

• TRACC

• TAU-II

• QUEST

• QuadGuard Elite (reusable)

Type VI – Gating, Non-Redirective Crash Cushions

• Does not redirect vehicles

• Sand is used to shield wide obstructions up to 13 feet

• Water is used in non-redirection and not in medians

with opposing traffic

NCHRP 350 Approved Type VI Terminals

• Energite III Module (sand)

• Fitch Universal Module (sand)

• Traffix (sand)

• ABSORB 350 (water)

o Proper anti-freezing agents must be used when the ABSORB 350 is used in areas where low temperatures can be expected

ABSORB 350

• REACT 350 & REACT350 (60")(reusable)

• SCI100GM and SCI70GM(reusable)

• QuadGuard LMC(extended reusable)

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Turndown End Terminals

• Should not be used on the National HighwaySystem (NHS)

• Should not be used on non-NHS roadways witha speed limit of 45 mph and above, and an ADTof 4000 and greater.

For further details see RC-52M, Sheet 3

Terminal Grading Details

A barrier terminal is most likely to perform best whena vehicle is stable at the moment of impact and thereis a traversable runout area immediately behind theterminal. Whenever practical, a barrier should beextended until these conditions can be met.

When a grading platform must be built it is critical thatit be designed and built to blend with the originalembankment and not cause instability in a vehiclebefore, during, or after a crash into the terminal. Thefollowing drawings show minimum gradingrequirements for parallel and flared terminals,respectively.

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PUB 6

52 2

010 E

ditio

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For further details see RC-54M Sheet 4

Grading Requirements for Terminals

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PUB 6

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For further details see RC-54M Sheet 4

Grading Requirements for Terminals

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Guide rail systems must be kept in good workingcondition (near to “as-built condition”) if they are tocontain and redirect impacting vehicles. Somedeterioration will occur as a result of crash damageand environment degradation. Much of this damagecan be considered “cosmetic” and will not measurablyaffect barrier performance. However, some kinds ofdamage may seriously degrade performance such asthose listed below in the Longitudinal Barrier Damageand Terminal Damage sections. Repairs to thesekinds of noted damage should be given priority.

The Department’s Maintenance Manual states,“Inspections should be made at least twice a year, inthe spring after snow season is over, and in the fallprior to the snow season. These inspections shouldbe concerned with alignment, appearance andgeneral condition. Any sections in need of repairs ormaintenance should be noted and scheduled forrepair by the County Manager.”

On interstates/expressways particular emphasis is tobe placed on completing necessary springtime guiderail system repairs by May 20th following the wintermaintenance season, especially those repairs thatcould not physically be made over the winter months.

In general, subsequent damage to guide rail thatfollows completed springtime repairs should also berepaired in a timely manner throughout the year. Thisincludes completing appropriate repairs orreplacements before the winter season begins and theability to address them is lost until the following spring.

Note, while it is not practical to quantitatively define “ina timely manner”, each identified, damaged barriersite needs to be assessed, prioritized and scheduledfor repairs based upon risk exposure (highway type,kind of barrier/terminal damage, potential for beingrestruck in the interim, etc.).

Part 4 - Maintenance

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Longitudinal Barrier Damage

These kinds of guide rail damage can result in inadequate structural and redirection performance:

• Vertical tears in the W-beam rail that begin at thetop or bottom edge. These are likely to result in railseparation in a crash.

• Similarly, holes in the rail resulting from damage ordeterioration that reaches the top or bottom of arail or one hole with a height greater than 1 inch orseveral holes with a height less than 1 inch withina 12.5-foot length of rail.

• More than 1 missing or ineffective splice bolt.

• More than 9 inches of lateral deflection over a 25-foot length of rail.

• Top rail height more than 2 inches lower than theoriginal rail height.

• Rail flattening that increases the W-beam sectionwidth from its original 12 inches to 18 inches or more.

Terminal Damage

These kinds of guide rail terminal damage can resultin inadequate end anchorage and engineered designperformance:

• Broken or damaged end post

• Missing or very slack rail-to-end post cable

• Missing bearing cable plate at end post

• Impact head not properly aligned with W-beam railelement.

• W-beam rail element not properly seated in impacthead.

Repair/Upgrade/Remove

When a guide rail or terminal is damaged to the pointwhere repairs are needed, several questions shouldbe asked before the damaged hardware is simply replaced in-kind:

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• Is the barrier warranted or could it be removed?

• Does the barrier meet current design standards orshould it be upgraded?

• Is the terminal an acceptable crash-tested design?(NOTE: the Breakaway Cable Terminal or BCTshould be replaced; the Modified Eccentric LoaderTerminal or MELT is considered crashworthy atspeeds up to 45 mph).

• If crashworthy, is the terminal the most appropriatetype for the location? (NOTE: Non-energy absorb-ing terminals require a significant traversablerunout area behind and parallel to the rail; energyabsorbing terminals require less runout distance).

• Turned-down terminals are not considered crash-worthy on the approach end of barrier installations.They are best used on the departure end of barrierruns, at STOP sign controlled entrances or at loca-tions where the chance of vaulting over the termi-nal is considered low.

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Guide Rail References

AASHTO (2006). Roadside Design Guide, 2006 Edition -https://bookstore.transportation.org/Item_details.aspx?id=148

FHWA (2005). Barrier Guide for Low Volume and Low Speed Roads,Publication No. FHWA-CFL/TD-05-009 -http://www.t2.unh.edu/nltapa/Pubs/barrier_guide.pdf

PennDOT (2009). Guidelines for the Design of Local Roads andStreets. Chapter 2. Publication 70M -ftp://ftp.dot.state.pa.us/public/bureaus/design/Pub70M/incover.pdf

PennDOT (2010). Standards for Roadway Construction, Publication 72M.ftp://ftp.dot.state.pa.us/public/Bureaus/design/pub72m/pub72cov.pdf

PennDOT (2009). Design Manual Part 2. Chapter 12. Publication 13M -ftp://ftp.dot.state.pa.us/public/Bureaus/design/Pub13M/insidecover.pdf

PennDOT (2010). Maintenance Manual. Chapter 11. Publication 23 -ftp://ftp.dot.state.pa.us/public/PubsForms/Publications/PUB%2023/PUB%2023.pdf

FHWA Policy/Guidance –http://safety.fhwa.dot.gov/roadway_dept/policy_guide/road_hardware

FHWA Longitudinal Barriers –http://safety.fhwa.dot.gov/roadway_dept/policy_guide/road_hardware/barriers/index.cfm

Roadside Safety Research Program Pooled Fund Study –http://www.roadsidepooledfund.org/

AASHTO Guide to Standardized Highway Barrier Hardwarehttps://bookstore.transportation.org/Item_details.aspx?id=161

Energy Absorption Systems Inc –http://www.energyabsorption.com/

Road Systems, Inc. – http://www.roadsystems.com/

Trinity Highway Products – http://www.highwayguardrail.com/

Nucor Highway Products – http://nucorhighway.com/

Gregory Highway Products – http://www.gregorycorp.com

Gibraltar - http://www.gibraltartx.com/

Brifen USA – http://www.brifenusa.com/

Barrier Systems, Inc. – http://www.barriersystemsinc.com/

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2010 edition - dot.state.pa.us 652.pdf · guide rail or are longer posts required? this document...

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