Civil Engineering Reference
In-Depth Information
Chapter 17
Adaptation Strategies for Managing
Recurring Congestion
—
Adding
New Capacity
17.1 Introduction
Most operational improvements provide gains in capacity. Important as they are,
they produce short-lived travel time reductions in areas with a growing population
and employment. In these cases the extra ef
ciency and travel time reductions
gained through operational improvements are soon lost as the growth in traf
c
demand reaches the capacity of the improved roads:
“
only so much extra ef
ciency
can be squeezed out of an already
[
1
].
Adding new roadway capacity is an effective strategy in reducing congestion. As
shown in Fig.
17.1
, areas that were more successful
—
stressed highway system
”
in adding road capacity
experienced a fraction (1/3
1/4) of the congestion growth found in areas less
successful in adding road capacity [
2
].
The reasons underlying the need for capacity expansion can be generalized as
follows:
-
Many urban roads are congested
—
even those where operational improvements
have been implemented
Long term growth will exceed the capacity gains resulting from operational
strategies
Newly developing areas will need improved roadway infrastructure
New and expanded major developments in existing cities and suburbs will need
new transportation infrastructure
Adding new roadway capacity to reduce existing and anticipated congestion can
be done in various ways. New roadways and lanes can be provided for all vehicles,
or they can be restricted to speci
c types of vehicles.
Examples of capacity strategies that apply to all vehicles include:
Bottleneck Reduction/Removal
Intersection Improvements
Street Connectivity/Continuity Improvements
