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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. 17-66
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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. 17-67
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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. 17-68
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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"). 17-69