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accessible travel modes to/from the areas concerned. If there is no acceptable
alternative to the use of a private vehicle, the car will continue to be the primary
transport mode, despite the enforcement of the parking policy. In the public's eye,
the travel mode is only a means of reaching a destination; it is not an objective in
itself. That is to say, if the travel mode is comfortable, fast, efficient, and affordable,
the travelers will use it, whether it is a private vehicle, public transit, or even a slow
mode such as a bicycle or even one's feet (Hansen
1959
;H
ยจ
gerstrand
1970
; Ingram
1971
; Levine and Garb
2002
; Geurs and van Wee
2004
).
Enforcing parking-policy measures aims at reducing the number of motor
vehicles on the roads, which in turn encourages the use of alternative modes.
This sequence will eventually lead to a new equilibrium between the alternative
transport modes and the environment. This means that the public's objections
to parking-policy enforcement should not deter municipal authorities from
administrating such policies. Public criticism should be stifled, though, only by
creating and improving other means of reaching destinations, such as public transit
or some slow mode (Kodransky and Hermann
2011
).
21.3 Methodology
The main hypothesis of this paper is that physical and economic aspects of parking
policy affect the demand for travel by private vehicle (and, consequently, impact on
VKT and total travel time), which has a direct effect on motor-vehicle air-pollutant
emissions. Thus reducing the amount of on-street and/or off-street parking and/or
raising parking fee will lead to a decrease in private VKT and, hence, to a reduction
in motor-vehicle air-pollutant emissions.
If this hypothesis is proved to be correct, then the use of parking policies could
improve the urban environment in terms of both air quality and transportation-
network performance variables. This is an important point to be mentioned, since
it could be argued that adopting urban land-use and transportation policies in order
to improve the urban environment, such as its air quality, may not advance both
environmental and transportation objectives (Van der Schaaf
2002
). Urban land-use
and transportation planners might then have to make a compromise between
(improved) air quality and (less) total travel time. Total travel time is usually the
more important variable for transportation planners, when the objective is to
achieve system efficiency based on the minimization of total travel time (Wardrop's
second principle
1952
).
21.3.1 Conceptual Framework
Figure
21.1
illustrates the basic interrelationship of the research components. Urban
form and transportation system influence private VKT and travel time. VKT and
travel time affect air-pollutant emissions from motor vehicles. The transportation
