Civil Engineering Reference
In-Depth Information
It is vital, therefore, that standards of tolerable congestion delay re
fl
ect the size
of the urban area and is developed from stakeholders
participation. When this is
done the products of transportation professionals will have a better chance of
in
'
fl
uencing the decisions that provide congestion relief.
24.5 Consequences of Congestion
The consequences of congestion include longer and less reliable journey times,
lower vehicle throughput, more crashes, reduced mobility and accessibility, and
increased travel and environmental costs.
24.5.1 Trip Time
Longer trip times and slower trip speeds are the most perceptible user impacts.
Because congested networks have a more adverse effect on longer trips, trip length
should be considered in congestion analysis.
24.5.2 Mobility
Trip mobility varies with the door-to-door speed of travel, and can be de
ned as the
number of trips taken and their distance (trip-miles) within the traveler
'
s daily travel
time and cost budgets. Lower traf
c speeds resulting from congestion reduce the
mobility of people who drive longer distances. The mobility of those who walk,
bike or use local public transportation is less impacted by congestion because
their trip lengths are shorter.
24.5.3 Accessibility
Accessibility is de
ned as the number of opportunities accessible from given
location within an acceptable travel time and cost budgets. Typically, it is deter-
mined by (1) a traveler
s mobility (the door-to-door distance one can cover within a
travel time and cost budgets), (2) the number of desired opportunities located within
this distance, and (3) the connectivity of the street network that determines the
directness of travel between an origin and a desired destination. The impact of
traf
'
c congestion on accessibility is often determined by land use density patterns
(density and mix) and design as it is by roadway network speed.
