This document discusses components of the traffic system including roadways and control devices. It covers five elements of the traffic system: users, vehicles, roadways, controls, and the general environment. Roadways provide accessibility for direct connection to land uses and mobility for vehicle movement. Control devices communicate traffic laws and regulations to drivers through markings, signs, and signals. The Manual on Uniform Traffic Control Devices (MUTCD) establishes standards for the application and design of control devices.

1. CE 436 Traffic Engineering
Topic 2: Components of the Traffic System
2B: Roadway and Control Devices
Prof. Saad AlGadhi
CE 436 –Traffic Engineering
King Saud University
email: salgadhi@ksu.edu.sa

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Traffic Stream
Components and Characteristics
Five Elements of Traffic System:
 Users (drivers, pedestrians, etc.): Ch.2
 Vehicles (private, commercial): Ch. 2
 Roadways: Ch. 3
 Controls: Ch. 4
 General environment (weather, lighting,
enforcement policies, etc.)

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Ch. 3: Roadways & its
Geometric Characteristics
 Roadways provide two primary services/functions:
 Accessibility: direct connection to abutting lands and
land-uses provided by roadways
 e.g. curb parking, driveway access to off-street parking, bus stops,
taxi stands, loading zones…
 Mobility: through movement of people, goods & vehicles
 These two functions are often in confilict
 This leads to the need to develop roadways in a
hierarchal manner; each class for a specific function

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Trip Functions
AASHTO defines 6 distinct possible travel
movements in a typical trip:
1. Main movement
2. Transition
3. Distribution
4. Collection
5. Access
6. Termination

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HWY Functional Classification
 Highway Classes:
 Limited-access facilities (e.g. Freeways)
 Arterials
 Collectors
 Local streets
 Freeway vs. Expressway (access control)

6. Hierarchy of Roadway Classifications

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Mobility vs. Accessibility

8. Through Service Provided by
Various Roadway Categories

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Service Function

10. Suburban Residential Subdivision

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Geometric Design of Highways
 Physical proportioning of facilities.
 Three main elements influence traffic
flow and operation:
 Horizontal alignment
 Vertical Alignment
 Cross-sectional elements
 These were covered in detail in CE 431.

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Ch. 4: Traffic Control Devices
 TCDs are the media through which traffic engineers
communicate with drivers: traffic laws, regulations,
or operating instructions
 They fall into three broad categories:
 Traffic markings
 Traffic signs
 Traffic signals

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MUTCD: Manual on Uniform
Traffic Control Devices
 MUTCD for streets and highways is the principal
standard governing the application, design, and
placement of TCDs.
 First attempt to create national standards for TCDs
occurred in 1927 by AASHTO
 First MUTCD was published in 1935
 Latest edition 2009 revised in 2012.

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MUTCD General Principles
 TCDs purpose is to promote highway safety and
efficiency by providing orderly movement of all
road users on streets, highways, public facilities, and
private property open to travel throughout the
nation.
 To be effective a TCD has 5 requirements. It must:
 Fulfill a need
 Command attention
 Convey a clear, simple message
 Command respect of road users
 Give adequate time for a proper response

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MUTCD Contents
 Detailed standards for the physical design of the
TCD, specifically shape, size, colors, legend types
and sizes, and specific legend.
 Detailed standards and guidelines on where devices
should be located with respect to the traveled way.
 Warrants, or conditions, that justify the use of a particular
device.
 It provides guidance and information in 4 categories:
 Standard (mandatory)
 Guidance (recommended)
 Option (permissive)
 Support (for info only)

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Communicating with the Driver
 A number of mechanisms are used to convey
messages to the driver, using recognized human
limitations, particularly w.r.t. eyesight.
 Messages are conveyed through the use of each of
the following elements:
 Color
 Shape
 Pattern
 legend

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Reading Materials
 Chapter 3, sec. 3.1
 Chapter 4, sec. 4.1