at-grade intersection
DESCRIPTION
At-Grade Intersection. Types of Intersection Maneuvers. Source: FHWA Roundabout Guide. 4-way Intersection. 32 conflict points. High speed impacts. High angle impacts. Roundabout. 8 conflict points. 75% reduction in Motor Vehicle conflicts. Low speed impacts. - PowerPoint PPT PresentationTRANSCRIPT
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At-Grade IntersectionAt-Grade Intersection
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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
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4-way Intersection
32conflict points
High speed impacts High angle impacts
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Roundabout
8conflict points
75% reduction inMotor Vehicle conflicts
Low speed impacts Low angle impacts
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BEFORE AFTER
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Intersection Control HierarchyIntersection Control Hierarchy• No Control (Basic Rule)• Yield Sign• Stop Sign – normal control method• All-Way Stop• Roundabout• Traffic Signal• Grade Separation
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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
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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!
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GRADE SEPARATION• High flows• Minimal delays• Expensive
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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)
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Traffic Lane
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Auxiliary Lanes
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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)
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Auxiliary LanesTapers
MEDIAN
MEDIAN
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Lane Shift
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Offset Left-Turn Lanes
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Offset Left-Turn Lanes
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Continuous Left-
Turn Lanes
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Minimum Design for U-TurnsExhibit 9-92
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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
e Pa
ths
Prom
otio
n of
Saf
e Sp
eeds
Sepa
ratio
n of
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
e fo
r Pe
dest
rians
Traffic Lanes Traffic Islands Median Dividers Corner Radii Approach Geometry Pavement Tapers or Transitions Traffic Control Device
Objectives of Channelization
Design Elements
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Design of ChannelizationDesign of Channelization
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Design of ChannelizationDesign of Channelization
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Design of ChannelizationDesign of Channelization
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Design of ChannelizationDesign of Channelization
90°
180°
120°
150°60
°
30°
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Design of ChannelizationDesign of Channelization
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Design of Channelization (Type 1)Design of Channelization (Type 1)
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Design of Channelization (Type 1)Design of Channelization (Type 1)
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Design of ChannelizationDesign of Channelization
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Design of Channelization (Type 2)Design of Channelization (Type 2)
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Design of Channelization (Type 2)Design of Channelization (Type 2)
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Design of ChannelizationDesign of Channelization
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Design of Channelization (Type 3)Design of Channelization (Type 3)
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Design of Channelization (Type 3)Design of Channelization (Type 3)
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Design of ChannelizationDesign of Channelization
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Design of Channelization (Type 4)Design of Channelization (Type 4)
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Design of Channelization (Type 4)Design of Channelization (Type 4)
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Design of ChannelizationDesign of Channelization
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Design of ChannelizationDesign of Channelization
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Traffic Island
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Simultaneous Left-Turn Lanes
Exhibit 9-99
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Corner CutCorner Cut
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Appendix
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Sight ObstructionSight Obstruction
Hidden Vehicle
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Auxiliary LanesAuxiliary Lanes
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3.0 - 4.8 m
Continuous Continuous Left-Turn Left-Turn
LanesLanes
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Offset Left-Turn Lanes
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Traffic IslandTraffic Island