Civil Engineering Reference
In-Depth Information
Chapter 24
Recap and Concluding Observations
24.1 Introduction
This topic has focused on metropolitan traf
c congestion in the US and Canada. Its
various chapters have described and analyzed the nature, causes, and consequences
of traf
c congestion in cities and suburbs, and they have set forth the various
strategies and actions that can be taken to provide congestion relief. This con-
cluding chapter summarizes the key
findings, gives guidelines for congestion
management and illustrates possible applications of congestion relief strategies in
different settings.
24.2 Types of Congestion
Congestion can occur each day at the same time and location along a street or
highway. This type of congestion is known as
“
recurring congestion.
”
A second
type of congestion is the
congestion that results from random
events such as vehicle breakdowns, crashes, inclement weather, natural disasters or
surges in travel demand. The US Federal Highway Administration indicates that
non-recurring congestion accounts for about half of the total traf
“
non-recurring
”
c delay in US
urban areas. This recognition, coupled with the fact that relieving recurring con-
gestion through added capacity has become increasingly difficult (high cost and
environmental constraints to capacity expansion) to implement, have led trans-
portation agencies to pay greater attention to reducing the delay impacts of non-
recurring congestion through the application of ITS tools.
