Portland State University Department of Civil

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Portland State UniversityDepartment of Civil
Environmental EngineeringCE 454Urban
Transportation Systems

• Intersection Control and Design

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Background
Table of Contents 1 Transportation as a
System 1 2 Transportation Economics 31 3 T
he Land-Use/Transportation System 61 4 Vehicle
and Human Characteristics 97 5 Traffic Flow
Characteristics 119 6 Geometric Design of
Highways 165 7 Highway Capacity 223 8 Int
ersection Control and Design 287 9 At-Grade
Intersection Capacity and Level of
Service 337 10 Public Passenger
Transportation 431 11 Urban Transportation
Planning 485 12 Local Area Traffic
Management 557 13 Energy Issues Connected
with Transportation 603 14 TSM Planning
Framework 631 15 Evaluation of Transportation
Improvement 667 16 Transportation
Safety 697 App. A Elements of Engineering
Economics 729 App. B Application of
Probability and Statistics 739 App. C General
Statistics on Transportation System and Use in
United States 775 App. D Conversion Tables for
Units of Measurement 795
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Background

• CE 351 left off dealing with capacity and level
  of service for uninterrupted flow facilities
  (freeways, rural two lane highways)
• Next look at interrupted flow facilities
• First must understand design and control
  principles of intersections.

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Introduction to Intersection Control
Objectives

• Understand why some sort of control is essential
  to allocate right-of-way at intersections
• Understand there is a hierarchy of intersection
  control (a traffic signal is not a panacea)
• Learn how to check sight distances available at
  an intersection
• Learn about the warrants for stop and yield
  controls
• Learn how to check traffic signal warrants

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Today

• Types of intersections
• Counting the number of conflicts at intersections
• Hierarchy of intersection control
• Method to check sight distances at intersections
• Warrants for STOP and YIELD signs
• Warrants for traffic signals

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Types of Intersections

• At-grade
• Three leg (tee, wye)
• Four leg (simplest two one way streets)
• Multi-leg
• Rotary
• Grade separation
• Crossing separated without connection
• Interchange
• Diamond (also tight diamond)
• Urban (single point urban)
• Directional
• Cloverleaf
• Partial Cloverleaf (parclo)
• Tee
• Wye

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Intersection Philosophy

• Miminize potential conflicts
• Vehiclesall modes
• Pedestrians
• Bicyclists
• Considerations
• Human
• Driving habits, decision/reaction time
• Traffic
• Demand, capacities, turning movements, delay,
  vehicle speeds, size and types of vehicles
• Physical
• Adjacent property, sight distance, geometric
  features, aesthetics, air quality, environmental
• Economic
• Cost, benefits, energy consumption

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Control Devices

• Control may be achieved by using traffic signals,
  signs, markings, or markers that regulate, guide,
  warn, and/or channel traffic.
• Manual on Uniform Traffic Control Devices (MUTCD)
• Detailed standards for the physical design of the
  device, covering size, shape, colors, legend
  types, and specific legend.
• Detailed standards and guidelines on where
  devices should be physically located or placed in
  relationship to the roadway.
• Warrants, or conditions which justify, the use of
  a particular device.

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Control Devices

• Requirements to make a traffic control device
  effective
• Fulfill a need ? Place proper device, only the
  one needed
• Command attention ?Make device stand out by
  color, shape, etc. (design)
• Convey a clear simple meaning ? Do not confuse
  driver with wordy legends only one instruction
  per device. (design)
• Command the respect of road users ?When you place
  it, you really mean it. (placement)
• Give adequate time for proper response ? Make it
  visible well in advance of decision point
  (placement)

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Control Devices

• Design
• (color, size shape to meet requirements
  above),
• Placement
• (within cone of clear vision),
• Operation
• (right device at the right place),
• Maintenance
• (to maintain legibility),
• Uniformity
• (provide uniformity in use of control devices).

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Control Devices

• SIGNS
• MARKINGS

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Assessing the Viability of Basic Rules of the Road

• Sight distance must be adequate before driver is
  held accountable for her actions.
• Check if adequate SSD is available.
• SSD must be satisfied before traffic volumes are
  considered.

Similar triangles
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Rule 1
Both vehicles have at least one safe SSD to the
collision point
Step 1 Assume Vehicle A is located one safe SSD
from collision point.
Step 2 Based on assumed position, find location
of Vehicle B when it first becomes visible. Call
it dB(act)
Step 3 Vehicle B must have one safe SSD. Call it
dB(min).
Step 4 If dB(act) lt dB(min), then adequate SSD
for has been provided. Otherwise, violated and
under Rule 1, not safe.
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Rule 2
Vehicle A must travel 18 feet past collision
point in same time that Vehicle B travels to a
point 12 feet before the collision point
dB
dA
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Sample Problem
Step 1
Step 2
Step 3
Step 4
dB(act) ltlt dB(min,R1) and dB(min,R2) Both rules
were violated.