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Parking Supply
The amount of parking provided as part of a TOD plays a critical role in its transportation outcomes.
A large quantity of parking reduces effective land use density and generally correlates with large
numbers of automobiles driving to and within the TOD, requiring accommodation on the roadways
in and near the development. On the other hand, a reasonable supply of parking for those who need
or want to drive is required to sustain development viability. Moreover, insufficient park-and-ride
parking at a TOD, without compensatory park-and-ride spaces elsewhere, can reduce transit rid-
ership by limiting the auto access ridership component. Yet, besides diluting density, excessive
parking can create a hostile environment for pedestrians and transit.
Contributing to these conflicts are the two separate markets for parking that exist at most
TODs--parking for the development at the station and parking for transit users. Each of these is
discussed here in the TOD context. In addition, many of the issues involved in TOD parking are
relevant to--and have been studied in the context of--many different types of urban areas. For
general topic coverage of development and station parking, respectively, see Chapter 18, "Parking
Management and Supply," and Chapter 3, "Park-and-Ride/Pool."
Development Parking
A TOD with proportionally more parking is likely to experience lower transit usage for accessing
the development than a TOD with proportionally less parking. This follows from the effect parking
scarcity has in serving to increase the disutility of driving and thereby improving the comparative
advantage of using transit or walking to reach destinations within the TOD. This disutility derives
from the time required to find or wait for an open parking space or from time spent accessing and
using parking facilities. The 2003 California TOD travel characteristics study found that higher
supplies of parking per worker were correlated with reduced transit commuting to station-area
offices. For offices with less than one parking space per two workers, a commuting transit mode
share of 30 percent was reported. For office projects with more than one space per two workers,
an average commuting transit mode share of less than 10 percent was reported (Lund, Cervero,
and Willson, 2004a).14
Parking requirements for serving the uses at a TOD are generally lower as compared to
conventional development for several reasons, including lower vehicle ownership by
residents, higher non-automobile mode shares, and more shared parking. Shared parking
refers to parking spaces serving multiple land uses with at least partially complementary
14
Office location undoubtedly affects the provision of parking supply, so the differential in commuting mode
share reported here likely reflects not only the influence of parking availability but also the various influ-
ences of locational differences including accessibility via transit.
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demands over the hours of the day, allowing each parking space to serve more than one land
use. (For more on shared parking, see "Shared Parking" within the "Related Information and
Impacts" section of Chapter 18, "Parking Management and Supply.") Although shared parking
does not directly impact transit usage, it can allow for a higher level of development density or
a more pedestrian-friendly layout as a result of reduced parking space requirements per unit of
development (Boroski et al., 2002).
No compilations have been encountered of direct observations of parking demand under TOD
conditions. Recently enhanced standard data sources are available, however, to assist in estimating
TOD parking requirements. The 3rd Edition of the Parking Generation informational report by the
Institute of Transportation Engineers (ITE) has begun a process of identifying parking demand
observations by various factors that potentially affect parking demand. It contains not only single-
use suburban development parking demand values but also some data obtained under urban
conditions. It also provides parking demand data linked to specific hour of the day, which can
assist in estimating the parking space reduction possibilities of shared parking, especially when
used in conjunction with the new 2nd Edition of the Shared Parking guide prepared by the Urban
Land Institute (ULI).
TOD versus non-TOD mode share observations provide one avenue for adjusting standard park-
ing rates. The ULI publication provides an analysis methodology that incorporates mode share
and trip capture in parking demand estimation. Practitioners advise that the suburban versus
urban parking demand values now available in ITE's 3rd Edition Parking Generation provide
indications of reduced parking demand with favorable modal options and mixed-use blends and
serve the useful purpose of bracketing the values likely appropriate for most TOD (ITE, 2004;
Urban Land Institute, 2005; McCourt, 2006).
Availability of these tools notwithstanding, parking demand based on actual parking-occupancy
surveys of TODs in comparison to non-TOD development remains an area needing further
research and evaluation. In the absence of observed TOD parking demands, Table 17-31 provides
a compilation of parking requirement reductions allowed TOD commercial developments, rela-
tive to standard non-TOD requirements, by various planning and zoning authorities across the
United States.15
Transit Parking
Some TOD is constructed entirely or in part on existing park-and-ride facilities. When
parking capacity is reduced below the demand, lower levels of drive-access transit ridership
may result. The impacted ridership may or may not be fully compensated for by shifts to
other transit access modes along with new ridership produced by the TOD. Some riders may
drive to their destination rather than continue to use transit. No before-and-after studies
15 It is reasonable to assume that most or all of the allowed parking reduction examples listed in Table 17-31
are with reference to local government parking requirements adopted prior to availability of the new ITE
and ULI parking publication editions described above. Also, the original parking code requirements relative
to which reductions were allowed may have been excessive even for average non-TOD development. A
number of studies have shown that suburban workplace parking supply, heavily influenced by parking code
requirements, typically exceeds the demand for parking. For additional information on these studies and
related analyses see "Response by Type of Strategy"--"Maximum and Minimum Parking Requirements"--
"Minimum Parking Ratio Outcomes" in Chapter 18.
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were encountered to quantify these effects. However, concerns about potential ridership loss are
presumably behind the transit parking replacement requirements that many agencies have. About
one-third (34 percent) of the transit agencies surveyed for this chapter reported having park-and-ride
space replacement policies.
Table 17-31 Commercial Parking Reductions Granted at Selected TODs
Location Land Use Parking Reduction
Pacific Court (Long Beach, CA) Retail 60%
Uptown District (San Diego, CA) Commercial 12%
Rio Vista West (San Diego, CA) Retail/Commercial 15%
Pleasant Hill (CA) Office 34%
Pleasant Hill (CA) Retail 20%
Dadeland South (Miami, FL) Office 38%
City of Arlington (VA) Office 48%-57%
Lindbergh City Center (Atlanta, GA) Speculative Office 19%
Lindbergh City Center (Atlanta, GA) Retail 26%
Lindbergh City Center (Atlanta, GA) Single Tenant Office Towers 29%-70%
Portland (OR) Suburbs a General Office 17%
Portland (OR) Suburbs a Retail/Commercial 18%
Note: a Calculated relative to maximums specified in Metro's Title 2 Regional Parking Ratios.
Source: Boroski et al. (2002).
About 70 percent of agencies with replacement policies reported requiring one-for-one replace-
ment (or more) of station parking lost to TOD construction (Evans and Stryker, 2005). However,
at least two large agencies, the San Francisco Bay Area's BART and the Washington Metropolitan
Area Transit Authority, are among those that now allow reductions in park-and-ride parking upon
introduction of TOD (Tumlin and Millard-Ball, 2006).
Two of the multiple regression research models developed for the 2003 California TOD travel
characteristics study, one of which was displayed in Table 17-28, found higher levels of
station-area parking to be related to higher average transit mode shares for station-area housing
projects. The finding, taken at face value, would suggest that such parking has a positive effect
on transit riding even among those living within walking distance. However, this somewhat
counter-intuitive finding could reflect limitations in the data set or analysis.16
Direct demand models for estimating rail station boardings generated by station area
population and employment provide additional insight. Two of these, developed on the
16 The "Relative [station] Parking Supply" variable in the two regression equations may, for example, be acting
to some degree as an unintended surrogate for exceptionally competitive transit service. Such transit service,
as in the example of HRT with its traffic-free operation, normally does come with large suburban park-and-
ride facilities. This concern makes it hard to judge the meaningfulness of the variable's positive coefficient
in assessing importance of station parking supply to residents within nominal walking distance.
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basis of BART HRT and Caltrain CRR data in one case and St. Louis Metrolink LRT data in the
other, contain a "number of station parking spaces" or equivalent variable. The two models have
station parking space elasticities of +0.038 and +0.045, respectively. The effect of parking is thus
shown again to be positive, but very weakly so in this context (Cervero, 2006).17 However, this
finding--which in approximate terms translates into an implication that 25 percent more station
parking spaces would be associated with roughly 1 percent more station boardings per day--does
not speak to the issue of what each individual park-and-ride space is worth in terms of ridership
in a location where it is or would be fully utilized. It looks at park-and-ride's contribution to rid-
ership in an overall context of stations with unconstrained, constrained, or no parking and with
multiple means of station access besides driving and parking.
Chapter 3, "Park-and-Ride/Pool," encountered very little quantitative analysis of the park-and-ride
space count's importance to ridership--an issue different than the question of how much park-and-
ride usage there is or might be. Park-and-ride patrons do constitute major proportions of ridership on
suburban rail and express bus systems in particular. Park-and-ride users tend to have higher incomes
and are inherently "choice" riders capable of readily electing to forsake transit if the mode is made
more difficult to use. Typically between 40 and 60 percent of park-and-ride patrons previously com-
muted by single-occupant vehicle. Each park-and-ride space in a fully utilized facility serves about 1.2
transit riders (2.4-or-more trips) per day. (For more on these observations, and citations, see the
"Prevalence of Park-and-Ride Activity," "Characteristics of Park-and-Ride/Pool Facility Users,"
"Prior Mode of Park-and-Ride/Pool Facility Users," and "Usage Characteristics of Park-and-
Ride/Pool Facilities" subsections under "Related Information and Impacts" in Chapter 3.)
Attracting (or losing) transit riders is, however, a little different than simply serving transit riders.
Studies in Connecticut of commuter rail rider response have estimated that a rough average of 0.2
transit riders are gained for each additional park-and-ride space added where parking supply is con-
strained (see "Response to Rail Park-and-Ride Facilities"--"Commuter Rail"--"Connecticut
Commuter Rail Park-and-Ride Lots" under "Traveler Response by Type of Park-and-Ride Facility"
in Chapter 3). The implication of this approximation is that when station parking is reduced many
riders will find another way to use the transit service, whether by walking further, getting dropped
off at the transit stop, parking at another station, or some other means. The specific estimate from
Connecticut applies to the unique New York City commutershed and is unlikely to have broad
applicability except as a general indication that the transit ridership impact of each park-and-ride
space may be significantly less than the observed utilization it receives. Of course, excess park-and-
ride spaces--if they exist or can be created through parking expansion or alternative access mode
improvements--have little or no ridership attraction or retention value.
The focus of these efforts to quantify park-and-ride space supply impacts has been on primary
mode share from a trip's origin to its final destination. Effects on mode of access choice are
also important. There is even less information available on this aspect. Automobile parking
infrastructure has been highlighted as a particularly important development design feature
largely neglected in travel studies and research (Ewing and Cervero, 2001). Large amounts of
17 An elasticity of +0.04 indicates a 0.04 percent increase in ridership in response to each 1 percent increase in
the variable, park-and-ride spaces in this case, calculated in infinitesimally small increments. These partic-
ular elasticities are true point elasticities (see "Concept of Elasticity" in Chapter 1, "Introduction," and
Appendix A, "Elasticity Discussion and Formulae").
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