The cost of congestion is the sum of individual costs of items that represent an
increase over normal operating costs directly attributable to the congestion. Among these
items are fuel and oil consumption, tire wear caused by the frequency and severity of
speed changes, other maintenance items affected by the speed changes, and increased
idling times. There are other costs that may not be readily apparent to the individual
driver but are real costs affecting the general public, such as inefficient movement of
commercial vehicles and the increased level of pollutant emissions.
Where congestion on freeways is of the recurring kind, the usual solutions to try and
solve the problem are geometric in nature. The most logical solution in many cases is
lane addition. In urban areas, congestion frequently occurs downstream from entrance
ramps when the combination of traffic entering the freeway and the traffic already
present exceeds the capacity of that segment. In other cases, the existing horizontal
alignment may contain one or more “sharp” curves, which result in lower capacity.
Ramp designs may have a detrimental effect on freeway capacity if their merge or
diverge areas are too short, or if they are too closely spaced, creating weaving problems
for traffic entering and exiting the freeway traffic stream. Other problems involving
physical features include unconventional interchanges, inadequate shoulders, narrow
medians, poor surface quality, and poor signing.
The next article discusses a new approach to the problem that takes advantage of
evolving technology: intelligent vehicle highway systems.