at-grade intersection types of intersection maneuvers source: fhwa roundabout guide
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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
Roundabout
8conflict points
75% reduction in
Motor Vehicle conflicts
Low speed impacts
Low angle impacts
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 Signals
Disadvantages
• 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!
At-Grade Railway CrossingsHorizontal alignment Intersection at right angle on a tangent section No other nearby intersections
Vertical 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)
Auxiliary Lanes
Auxiliary lanes:– remove accelerating or decelerating vehicles
from the through lanes – store turning vehicles– increase road capacity
Types of acceleration or deceleration lanes
parallel lanes
directional lanes (tapers)
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