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SA Page 41 The generous parking capacity required by planners often goes unused. Studying office buildings in ten California cities. Richard Willson (1995) found that the peak parking demand averaged only 56 percent of capacity. Gruen Associates (1986) found that peak parking demand at nine suburban office parks near Philadelphia and San Francisco averaged only 47 percent of capacity, and that no office park had a peak parking demand greater than 60 percent of capacity. The Urban Land Institute (1982, 12) found that the recommended parking requirements for shopping centers provide a surplus of parking spaces for all but nineteen hours a year, and leave at least half of all spaces vacant for more than 40 percent of the time a shopping center is open for business. Given the way planners predict parking demand. unused parking spaces are unsurprising. For example, an office building may first serve as a corp~rate headquarters with 300-square-foot offices for executives, and then be used by a telemarketing firm with 30-square.foot cubicles for telephone sales personnel. Fitting more employees into a building by reducing the office space PARKING GElERAnON RATES per person can greatly increase I ~ RIII,uf == fUrt/lft of A~af I parking demand. Surveying 57 ~ SIudiII suburban employment centers in the 0.52 0.20-0.88 . ~ I" United States. Robert Cervero (1988, 26) found that building occupancies DATA PLOUNDEOUAllOH ranged from 0.5 to 6.0 persons per ~_CUIOIUI'-4.OI' "MfDSlMlLSoUIU_ 1,000 square feet, with a standard 130 deviation almost as large as the mean. Q Given this 12-fold range of possible '30 53 building occupancy, how can urban ~ "0 D planners predict the number of parking a 'GO ~ spaces any office building will need III 1IO throughout its economic life? I eo [The chart to the left] shows a typical I 7lI page from Parking Generation (ITE . 1987, 44). It reports all the case .. eo studies of peak parking demand " observed at non-convention hotels. to flIO 120 ,~ '10 I8t JOO' . aD r.co Given the variation in observed peak \ parking demand (ranging from 0.29 to II . NUllIlfll 01' /lOOMS 0___ - ,..e..o 0.68 parking spaces per room), what is NldQM~".UJ\Il.~ an urban planner to say when asked to "'.0. set the minimum parking requirement for a hotel? The average peak parking demand is 0.52 spaces per room. To be safe. why not require 0.68 spaces per room, the highest demand observed? Maybe 0.75 spaces per room will appear less arbitrary. One space per room also looks plausible. In a recent survey, the Planning Advisory Service (1991, 16) reports eight cities' parking requirements for hotels: two cities require 0.75 spaces per room. two require 0.9 spaces per room, and four require one space per room. In setting minimum parking requirements, planners seem to play it safe. To help planners set parking requirements, the Planning Advisory Service (1964,1971,1991) has published three national surveys of parking requirements in zoning ordinances. These surveys tell planners only what other cities have required, not what they ought to require. According to the second survey (PAS 1971, 1): The implicit assumption is that other areas must know what they are doing (the ordinances were adopted, after all) and so it is a relatively safe bet to adopt a parking standard "dose to the average." This may simply result in a repetition of someone else's mistakes. Nevertheless, the planner who needs to present a numerical standard by the next planning commission meeting can't answer the original question by saying, "I don't really know." 1>~g,~ ~'1 ___...._ o'M__'.. ._---.~...-..,,_. .-. ..'-"'-""'~ -- -'---'~-'--'-"'.' ".-- .-- ...,.---. ._~---- - ,.--. ".,,_.'~_.,"