Civil Engineering Reference
In-Depth Information
Table
3.1
displays the peak period travel speed for the top ten corridors with the
longest peak period delay in 2010. These ten corridors are located in the largest
metro areas: Los Angeles, NYC, Chicago, and Washington, DC, and range in
length and speed from 11.3 miles at 15.8 mph (NYC: the Cross-Bronx Expressway
corridor), to 23.9 miles at 26.6 mph (Washington: I-95 southbound, from I-395 to
Russell Road).
There were 341 congested corridors nationwide in 2010, with a total collective
length of 2,295 miles. The average congested corridor (6.7 miles in length) operated
with a peak period speed of 26.8 mph. But there is a large variance from these
average values within metro areas in the same population groups, as well as
between groups of different sizes.
The characteristics of congested corridors vary widely among metropolitan areas
in
extent
(number and length), and
intensity
(average speed)
—
(INRIX 2010). This
variability is mainly related to the size of the urban area.
The largest areas (population of over 5 million) have the largest number of
congested corridors (Fig.
3.9
) and the longest (Fig.
3.10
).
It will be noted that a small number of corridors are congested in metropolitan
areas of
½
to 1 million people, and none are found in areas smaller than
½
million.
3.4 Summary and Outlook
Traf
c congestion in US cities is a byproduct of their success in attracting people
and jobs, and amenities. When growth in economic activities signi
cantly outpaces
the growth in transportation infrastructure investments, cities experience congestion
to levels that make mobility dif
cult.
Congestion is a consequence of where we live and work, how and where we
travel, and how land is used. It impacts travel cost, the quality of our air, traf
c
safety, and the fuel consumed by motor vehicles.
Urban growth is likely to continue for the rest of the 21st century. More people
are expected to live in metropolitan areas where they will occupy more land and
will travel further to dispersed places of work, shopping, and recreation. The
population and employment density gradients will continue to
meaning
population growth in outlying areas will continue to occupy more land at low
density; even as central cities are likely to grow, and the costs of car ownership and
driving are likely to increase. Congestion will follow these gradients: increasing in
outlying areas and permeating the weak links of the roadway system. Thus freeway
and suburban arterial congestion is likely to increase, extending outwards along
with land development. Longer trip lengths will place greater traf
fl
atten
—
c pressure on
many arterial roads and freeways.
Reducing congestion growth in large urban areas will require the
joint
imple-
mentation of concerted and consistent initiatives that (1) will increase transportation
ef
c
demand through higher land use densities, encourage growth along existing transit
ciency and capacity through new technologies, (2) will reduce automobile traf
