The following guidelines have been prepared to assist transportation engineering personnel in gathering and documenting basic parking generation data. These guidelines are intended to be used in conjunction with the parking demand survey form downloadable Excel spreadsheet.
Site selection is critical in achieving representative and consistent parking generation rates. Failure to select sites appropriately may lead to inaccurate parking generation rates and equations. Use of unrepresentative sites as a basis for parking generation estimates can result in overestimating or underestimating the number of parking spaces to be needed by the development.
Historically the parking generation data has been dominated by isolated, suburban sites in the United States and Canada. With continued updates to Parking Generation Manual, we encourage the submission of data for sites with a variety of characteristics (active TDM, heavy transit use, downtown, shared parking, mixed-use, bicycle parking, sites with parking cost, as well as isolated, free-standing single-use sites).
However, as site selection for a land use moves away from an isolated site, it is most important to clearly identify all locations where potential parking demand may be occurring (such as on-street parking, shared parking areas, adjacent lots, remote employee lots or other locations where significant parking demand may be occurring which is not in the immediate site parking facility).
Suggested criteria for identifying sites are as follows:
Permission to conduct a parking generation survey should always be requested from the owner/manager of a prospective survey site. The purpose and details of the survey should be fully explained. An offer should be made to share the results of the survey with the owner/manager.
Provision of an independent variable is essential to estimating parking demand ratios. Physical and functional characteristics of the site (e.g., number of acres, gross floor area, number of employees), that are not evident from a site inspection may be obtained from the owner/manager. Other sources of site data may include developers, architects, planners, government offices, consultants, realtors, assessors, or the home office of the development. The owner/manager should be able to furnish details of transit service and utilization of car or van pools. The owner/manager should also have a good idea of the days and hours of peak parking demand. An important statistic for the surveyor to ascertain is the occupancy of the site under study. The percentage of office space being utilized, the number of apartment units occupied, the number of spectators at a sporting event, etc., have a direct bearing on the parking generation rates. If all of the data cannot be obtained, provide as much as possible and complete the survey.
For a shopping center, it has been found that parking demand can vary significantly with the percentage gross square feet devoted to restaurant or entertainment activity. This additional variable should be collected as part of the survey and recorded in the data forms under "Notes". Restaurants would include any eating/drinking establishment, fast food restaurant or other food service-related activity. Entertainment would include any theater space, amusement park, night club or other entertainment activity. This information should be provided with any shopping center (land use codes 820, 821, and 822) survey, shown as a percentage (%) of the total gross square feet of shopping center area.
The objective of the survey is to count the number of vehicles parked at the time of peak parking demand. It is valuable to provide parking demand data for other hours of the day to establish the variation of parking demand over the hours of the day, but observation of peak parking demand should be the objective of each survey.
Usually, one can predict when peak parking accumulation will occur. Examples would include:
Peak parking accumulation at other types of land uses may be uncertain. These may require spot counts at specified intervals such as every one-quarter, one-half, one, or two-hour intervals throughout the day or portions of the day in order to assure accurate data. While multiple observations may be performed in one hour, only the highest observed parking demand for each hour should be entered on the parking demand survey form. Correlating the parking demand observation to the hour of day that the survey was conducted is a critical element of the parking generation data. The parking survey should also be sensitive to the fact that land uses may exhibit different parking trends from day to day. For example, a sales-oriented office may show higher parking demand on Monday mornings and Friday afternoons than during the mid-week when the sales force is out of town. List all information on the parking demand survey form including any observations or characteristics of the site that would be of interest. The web-based data entry form asks questions with pull-down selections about site characteristics that are important for consideration of parking demand (e.g. parking costs, type of surrounding area, etc.).
Many agencies and consultants have existing parking occupancy survey data on file. You are urged to use that data and fill out the survey form so that as much data as possible can be available in the ITE database. Again, it is not imperative that all data questions be answered; provide as much as possible and forward the data to ITE.
New parking demand surveys are needed to enhance the statistical value of the parking generation data. It is highly recommended that when a trip generation survey is conducted for a site, parking demand observations also be performed.
Data for this publication are being collected continually. To be considered for inclusion a future edition of Parking Generation Manual please submit data ITE, 1627 Eye Street, NW, Suite 550, Washington, DC 20006 USA; fax to +1 202-785-0609 or parkgen@ite.org.
There are three methods for submitting data to ITE: