Civil Engineering Reference
In-Depth Information
to that of the existing community center. While the new perimeter road increases
accessibility for all four centers, the largest increase is shown for the new inter-
changes (A, B, C) and the lowest for the existing center
[
16
].
In larger metropolitan areas, freeway systems account for about 50 % of all
vehicle miles of travel
“
O
”
—
even though they provide only a small fraction of the total
lane miles.
One key question regarding the congestion relief bene
ts provided by added
new freeway capacity is the is the issue of
both in the short
term, as travelers make longer or more frequent trips; and in the long term, as
people and businesses make location decisions that may lead to additional travel.
This issue is discussed in Sect.
17.4
.
In his 1979 topic Urban Transportation System
“
induced demand
”—
Politics and Policy Innovation,
Alan Altshuler summarized the congestion reduction bene
—
ts of road capacity
enhancement:
What seem clear is that even over the long run, areas that invest
heavily in road capacity seem to maintain higher speeds than areas that do not. Their
main arterials may in time become heavily congested during peak hours, but they will
normally continue to operate at higher speeds than older, unimproved roads
“
”
[
17
].
17.3 New Capacity Strategies for Priority Vehicles
Capacity expansion strategies for
have emerged over the last
quarter century in response to congestion and environmental concerns. The
“
priority vehicles
”
“
pri-
ority vehicles
lanes include Managed Lanes (HOV, HOT, Express Toll), Truck-
only Lanes, and Intermodal Access Roads.
The goals of these lanes are to (1) provide greater people-carrying capacity,
(2) increase roadway productivity in person
”
miles per hour, (3) maintain corridor
mobility as travel demand continues to increase, and (4) reduce the number of
single occupant vehicles.
—
17.3.1 Managed Lanes (HOV, HOT, Express Tolls)
Managed lanes on freeways and arterial roads work best where there is extensive
traf
ca-
tions, frequent bus service, and suitable ways to enter and leave the managed lanes.
Strong traf
c congestion, adequate roadway geometry that can adapt to needed modi
c generators such as the city center and other outlying centers along the
corridor are essential.
Managed lane treatments vary by type of facility (freeway or arterial streets),
substantial volumes of eligible vehicles (buses, car pools, and or trucks), methods
of operations (concurrent or contra-
ow), hours of operation, and availability of
ancillary facilities (park-and-ride lots or garages), toll collection infrastructure, and
pricing.
fl
