Civil Engineering Reference
In-Depth Information
Table 23.2 Population density versus traf
c density for the San Francisco bay are
Location
Population density
(persons per acre)
VMT per capita
(vehicle
Traf
c density
(daily VMT per acre)
miles per
person per day)
—
Healdsburg
5
30
150
Berkeley
30
10
300
Downtown San
Francisco
250
4
1,000
Source
Created by Prof. Martin Wachs in Reference [
3
], p 15
less traf
c congestion, but provide travelers with more travel options. Traveler
bene
ts of high density include the availability of alternative modes to the auto-
mobile, and a higher number of destination opportunities accessible by alternative
travel modes.
23.2.3 Densities for Public Transit
Many studies have shown that increasing population and employment densities
produce higher shares of transit trips. As population density increases, the
number
of person trips made by public transportation (including pedestrian trips) increases.
Conversely as densities decline, travel demands become more dispersed and transit
becomes less effective in serving this demand. Public transit works best where
travel is concentrated in time and space. It is well suited to serve high employment
and population densities.
The best transit markets are found where
both
employment and population
densities are high
Higher residential densities and lower auto ownership per household results in a
higher proportion of regional and CBD trips by transit
The proportion of CBD trips by public transport increases as employment
density rises. For example, more than 90 % of all peak period person trips to the
Manhattan CBD (NYC), where employment density approximates 800 persons
per acre, use public transportation. In contrast, about 20 % arrive by transit in
Denver (CO), where downtown employment approximates 150 persons per acre
[
4
]
Rapid transit and commuter rail relate closely to the number of jobs in the city
center
The likelihood of commuting by public transit as a function of residential density
and car ownership is shown in Fig.
23.1
.
Mixed use and high-rise developments offer the highest likelihood of transit use,
but use declines with increasing car ownership levels.
