Civil Engineering Reference
In-Depth Information
Fig. 3.8 A congested modern freeway.
Source “
“Traffic congestion and long commutes cost us
dearly in time and fuel
”
A 1970 study [
4
] of mobility in some 17 cities, found that traf
c speed increased
in 13 cities and decreased in four. Speeds increased more than 15 % in 8 cities
and decreased by more than 15 % in two.
In Los Angeles, despite a tripling of motor vehicle registrations between 1936
and 1967, off-peak travel times between the central business district (CBD) and
fourteen outlying locations declined from an average of 33
26 min, largely due
−
to continued freeway development.
Freeway construction in Los Angeles dramatically reduced traf
c on local
streets. For example, the daily traf
c on S. Figueroa Street declined from 45,000
vehicles in 1955 to 13,500 vehicles in 1958. But it has since been reported to
increase again (to over 34,000 in 1993) as a result of increased congestion on the
parallel freeway [
5
].
Peak hour speeds in Downtown Providence increased from 5
−
10 mph in 1927,
to 10
-
19 mph in 1978 [
6
].
In Boston, motor vehicle traf
c into and through the CBD increased by 80 %
from 1927 to 1960. Nonetheless average daily speeds on nine major downtown
streets increased from 10.5 to 13.3 mph
—
a 27 % increase over the period.
A one-way pattern established on north-south avenues in Manhattan produced a
travel time saving of 22 % for north-south traf
c, a 40 % savings for cross-town
traf
c, and a 20 % reduction in pedestrian accidents [
7
].
