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

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 under estimating the number of parking spaces to be needed by the development.  

Excel Spreadsheet

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:

• Data should be transferable; therefore, it is critical that both parking data and development characteristics be representative of the land uses to be analyzed.
• The development should have reasonably full occupancy (i.e., at least 85 percent) and appear to be economically healthy. The percent occupancy at the time of the survey is important, and should therefore be recorded.
• The development should be mature (i.e., at least two years old) and located in a mature area.
• The site should be selected on the basis of the ability to obtain accurate parking demand data for the land use under consideration.
• Locations where total parking demand can clearly observed for the selected land use (this may include not only the on-site parking lot/facility, but other shared/remote lots and/or on-street parking)
• There should be minimal or no on-site construction or adjacent roadway construction.
• Permission should be obtainable from the owner/manager of the prospective survey site.
• The use of a site vehicle trip generation count (comprehensive in/out observations) to create observed parking demand is acceptable only if:
  1. site parking demand was observed immediately before and/or after the trip generation counts; and
  2. there is no potential for through trips or other trips within the trip generation counts (such as significant vehicle, transit or truck trips of other sites).

Permission of Owner/Manager of Site

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.

Background Data

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 shopping centers 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 code 820) survey, shown as a percentage (%) of the total gross square feet of shopping center area.

Procedure

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:

• residential land use would generally peak at night or very early in the morning,
• restaurants at meal times (noon time and dinner time),
• office or employment uses typically peak in the mid-morning or mid-afternoon, and
• stadiums during capacity crowd events.

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 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 (eg. parking costs, type of surrounding area, etc…). For sites with complex characteristics (TDM, extensive transit use, shared parking, bicycle parking) a separate web-data entry form is being developed (under construction at this time).

Existing Data

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 data warehouse of parking generation. Again, it is not imperative that all data questions be answered; provide as much as possible and forward the data to ITE.

New Surveys

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, that parking demand observations also be performed. ITE is working cooperatively with universities and ITE Student Chapters to conduct parking demand surveys on an annual basis. For information regarding this program, please contact Jina Mahmoudi at jmahmoudi@ite.org.

Data Submission

There are three ways to submit parking data. The Excel spreadsheet is the preferred method of submission. However, if a prior study was completed with all the required background data, those studies can be submitted via mail to ITE at:

Parking Generation Survey
Institute of Transportation Engineers
1627 Eye Street, NW, Suite 600
Washington, D.C. 20006

 If you have any questions, do not hesitate to contact Jina Mahmoudi .