Civil Engineering Reference
In-Depth Information
Fig. 3.7 Gratiot Avenue, Detroit 1940.
Source
Automotive safety foundation
Traf
c engineering control methods alone could not keep up with the growing
traf
c demands. Congested conditions in cities were eventually alleviated by the
freeway construction associated with the Interstate Highway system. Many cities
built radial freeways with central area freeway loops that diverted through traf
c
from city streets. But route convergence, lane balance and close interchange
spacing led to operating problems and recurring congestion that has overwhelmed
many of these freeways for years. Over the years (1960-mid 1970s), however, the
combined effects of freeway construction and traf
c engineering improvements
alleviated traf
c congestion in many communities.
c congestion has increased continuously since the mid-1970s. It has largely
shifted from city center to suburbs, from city streets to suburban highways and
expressways (Fig.
3.8
).
A few studies have documented these improvements although systematic mea-
sures of congestion and mobility changes over the years have been lacking. Some
examples of reported improvements are given below:
Traf
