Civil Engineering Reference
In-Depth Information
for future growth, and to strengthen the viability of the city center and other mega
centers.
Some speci
c bene
ts of major transit projects include:
Expanding transportation capacity in a constrained environment/space. Transit
facilities occupy 1/4 of the space needed for freeways.
A transit
“
lane
”
can serve as much as 10
15 times the number of person trips
-
served by a freeway lane.
Allowing employment growth in the city center and other mega centers without
increasing street traf
c and parking requirements
Simplifying surface transit routes by feeding bus lines to rapid transit stations
and by reducing bus traf
c in congested areas
Providing more reliable trip times, since many causes of congestion are elimi-
nated. Rail speeds are twice or more the speeds attained on surface transit routes
Attracting auto users from heavily traveled congested corridors
Helping to structure land development around both urban and suburban stations
ts could often offset the high transit development costs and envi-
ronmental impacts normally associate with
These bene
fixed guide-way transit facilities. Thus
there should be a realistic balance between costs and bene
ts.
23.5.2 System Extensions
Market demand, political, physical, congestion factors and operating conditions
determine how far transit line should extend or be extended. Basic guidelines
include the following: (1) the length of the initial segment should be as short as
possible to provide the desired service and to attract the needed ridership. Once the
line is opened and its ridership is established, it then can be extended; (2) it should
be long enough to provide a few good stations at its outer end that could develop
the desired ridership; (3) the line should extend out far enough so that suf
cient
park-and-ride facilities can be provided at outer stations; and (4) it should serve
existing riders and should capture new riders as well.
Ideally, line coverage and station spacing should capture
both
existing and future
transit markets. New lines should extend beyond the limits of existing development
and right of way should be preserved or assembled for subsequent extensions. Many
successful lines and transit markets did not exist when some lines were initially built.
This is apparent from the evolving population density pro
les shown in Fig.
23.3
.
Residential densities in New York, Chicago, Philadelphia, and Boston clearly
re
first half of the 20th century. In
these cities the density patterns were similar. Rail transit lines had their greatest
impact on development around stations located in undeveloped areas
farthest
from
the city center, and not previously served by public transportation. Buildings were
fl
ect the result of rail transit development over the
