At-Grade IntersectionAt-Grade Intersection

Types of Intersection ManeuversTypes of Intersection Maneuvers

Source: FHWA Roundabout Guide

RIGHT LEFT MUTUAL MULTIPLE

RIGHT LEFT MUTUAL MULTIPLE

DIRECT OPPOSED OBLIQUE MULTIPLE

ELEMENTAL MULTIPLE

ELEMENTAL

DIVERGING

MERGING

CROSSING

WEAVING

4-way Intersection

32conflict points

High speed impacts High angle impacts

Roundabout

8conflict points

75% reduction inMotor Vehicle conflicts

Low speed impacts Low angle impacts

BEFORE AFTER

Intersection Control HierarchyIntersection Control Hierarchy• No Control (Basic Rule)• Yield Sign• Stop Sign – normal control method• All-Way Stop• Roundabout• Traffic Signal• Grade Separation

Traffic SignalsTraffic Signals

AdvantagesAdvantages• Orderly movement of traffic• Reduces certain types of crashes• Interrupts heavy flows for minor

movements• Promotes driver confidence• Provides gap for minor movements

Traffic SignalsTraffic SignalsDisadvantages• Increases total delay, especially off-peak• Increases fuel consumption• Increases crashes• Induces road users to less appropriate

routes• Unnecessary delay if not properly located• Bad timing, bad engineer!

GRADE SEPARATION• High flows• Minimal delays• Expensive

At-Grade Railway CrossingsHorizontal alignment Intersection at right angle on a tangent section No other nearby intersectionsVertical alignment Intersection as level as possible Adequate view of crossing Vertical profile should prevent vehicles with low

clearance from being caught on the track (see below)

Traffic Lane

Auxiliary Lanes

Auxiliary LanesAuxiliary lanes:

– remove accelerating or decelerating vehicles from the through lanes

– store turning vehicles– increase road capacity

Types of acceleration or deceleration lanesparallel lanes directional lanes (tapers)

Auxiliary LanesTapers

MEDIAN

MEDIAN

Lane Shift

Offset Left-Turn Lanes

Offset Left-Turn Lanes

Continuous Left-

Turn Lanes

Minimum Design for U-TurnsExhibit 9-92

Objectives of Channelization and Design Objectives of Channelization and Design Elements to Achieve ThemElements to Achieve Them

Proh

ibitio

ns o

f M

ovem

ents

Defin

ition

of V

ehicl

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ths

Prom

otio

n of

Saf

e Sp

eeds

Sepa

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Con

flicts

Angl

es o

f Cro

ss a

nd

Mer

ge

Facil

itatio

n of

Hig

h Pr

iorit

y M

ovem

ents

Facil

itatio

n of

Tra

ffic

Cont

rol

Acco

mod

atio

n of

Slo

w or

Dec

eler

atin

g Ve

hicle

sSa

fe R

efug

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dest

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Traffic Lanes Traffic Islands Median Dividers Corner Radii Approach Geometry Pavement Tapers or Transitions Traffic Control Device

Objectives of Channelization

Design Elements

Design of ChannelizationDesign of Channelization

Design of ChannelizationDesign of Channelization

Design of ChannelizationDesign of Channelization

Design of ChannelizationDesign of Channelization

90°

180°

120°

150°60

°

30°

Design of ChannelizationDesign of Channelization

Design of Channelization (Type 1)Design of Channelization (Type 1)

Design of Channelization (Type 1)Design of Channelization (Type 1)

Design of ChannelizationDesign of Channelization

Design of Channelization (Type 2)Design of Channelization (Type 2)

Design of Channelization (Type 2)Design of Channelization (Type 2)

Design of ChannelizationDesign of Channelization

Design of Channelization (Type 3)Design of Channelization (Type 3)

Design of Channelization (Type 3)Design of Channelization (Type 3)

Design of ChannelizationDesign of Channelization

Design of Channelization (Type 4)Design of Channelization (Type 4)

Design of Channelization (Type 4)Design of Channelization (Type 4)

Design of ChannelizationDesign of Channelization

Design of ChannelizationDesign of Channelization

Traffic Island

Simultaneous Left-Turn Lanes

Exhibit 9-99

Corner CutCorner Cut

Appendix

Sight ObstructionSight Obstruction

Hidden Vehicle

Auxiliary LanesAuxiliary Lanes

3.0 - 4.8 m

Continuous Continuous Left-Turn Left-Turn

LanesLanes

Offset Left-Turn Lanes

Traffic IslandTraffic Island