Civil Engineering Reference
In-Depth Information
Chapter 1
Introduction
1.1 The Nature of the Problem
Congestion in transportation facilities
—
walkways, stairways,
roads, busways,
railways, etc.
happens when demand for their use exceeds their capacity.
Travelers tend to complain about traf
—
c congestion because it adds to their travel
time and takes away from the time they can dedicate to other activities. Truck
drivers complain because it reduces their productivity and increases their operating
costs. Transit service providers complain about roadway traf
c congestion because
it increases the number of buses and drivers needed to provide the service. Con-
gestion increases business costs, air pollutant emissions and fuel consumed.
Congestion also can in
uence investment decisions, and therefore it becomes a
major economic concern. It in
fl
uences where people live, work and how they travel.
Therefore reducing congestion bene
fl
ts a wide constituency.
c congestion has been a fact of city life from ancient times when movement
was by walking and animal-drawn coaches to today
Traf
s cities that rely on various
means of mechanized travel. It is a byproduct of economic activities that grow
faster than the growth in transportation infrastructure.
Traf
'
c congestion is now found in cities throughout the world. It continues to
increase as the cities
population and motorization grow and as travel growth
outpaces investments in roads and public transportation. The beginning of con-
gestion is generally perceived by drivers when their trip time increases by
approximately 0.4
-
0.5 min/mile, and they become acutely aware of congestion
when it increases by 0.8
'
1.0 min/mile.
-
Traf
c congestion may also be the hallmark of a vibrant economy: a city without
a traf
c congestion problem is likely to experience an economic recession, or a
declining population. But where congestion is too pervasive and trip time reliability
is a problem, the city may become a less desirable attraction for economic growth.
