Civil Engineering Reference
In-Depth Information
transit service is available, the site design of buildings in these regional centers is
usually focused around parking access and not on transit access to the
“
front doors
”
of buildings.
Moreover, most suburban developments are mandated by building codes to
provide a minimum number of parking spaces per unit
floor area of building space.
This policy results in a network of parking lots and garages, interspaced between
of
fl
ce and commercial buildings, all connected by a network of local and arterial
roads. As a result,
“
suburban gridlock
”
is common both on freeways and some local
streets [
3
].
City size also affects traf
c congestion. Larger urban areas are generally more
congested than smaller ones. This condition results from both longer travel dis-
tances and larger concentrations of activities (as in the city center).
5.3 Paradox: Reducing per Capita Auto Use Increases
Trafc Congestion
Often the debate about urban traf
c congestion is framed around the need to reduce
widespread use of the personal motor vehicle
and
to increase the use of various
public transportation alternatives. One demonstrated way of reducing the depen-
dency on car use is to
increase
the density of land development.
Table
5.4
shows that as densities rise,
there are more walking and public
transport trips that decrease per capita VMT.
Table 5.4 Average daily travel per person in the united states by population density and mode,
1990 NTPS survey
Density range
(persons per
square mile)
Daily person trips by mode
Daily
person
miles
Daily
VMT per
person
Auto Bus Rail
Taxi Walk/
bike
Other Total
0
99
3.35
0.02
0.00
0.00
0.24
0.16
3.77
31.58
21.13
-
100
-
249
3.50
0.02
0.00
0.01
0.24
0.13
3.90
29.95
20.73
250
499
3.53
0.02
0.00
0.00
0.29
0.12
3.96
29.33
20.40
-
500
749
3.52
0.03
0.00
0.00
0.21
0.12
3.88
29.00
20.99
-
750
-
999
3.44
0.05
0.01
0.01
0.26
0.13
3.90
26.25
18.35
1,000
-
1,999
3.48
0.03
0.01
0.00
0.23
0.11
3.86
26.17
18.63
2,000
2,999
3.46
0.06
0.01
0.00
0.28
0.11
3.92
23.45
19.04
-
3,000
3,999
3.34
0.06
0.02
0.01
0.29
0.09
3.81
24.11
16.89
-
4,000
-
4,999
3.51
0.05
0.01
0.00
0.30
0.08
3.95
24.77
17.24
5,000
7,499
3.29
0.09
0.02
0.01
0.36
0.06
3.83
24.56
16.28
-
7,500
9,999
2.92
0.11
0.05
0.02
0.45
0.07
3.62
20.59
14.15
-
10,000
-
49,999
1.90
0.29
0.21
0.03
0.95
0.04
3.42
17.02
8.73
50,000 or more
0.59
0.42
0.61
0.16
1.55
0.07
3.40
12.55
2.31
Source
Reference [
4
], pp 15
21. Table
15.5
-
