Chapter 12

The collection of parking data has traditionally been conducted to address parking supply/demand, utilization, and turnover issues as part of the transportation planning process. However, as travel demand models have become increasingly sophisticated, parking surveys are also being used to provide additional travel behavior data for input into the modeling proc­ess. For example, parking generation surveys can improve the travel model calibration process by identifying and matching the demand and supply of vehicle trips generated to and from parking facilities located within specific traffic analysis zones (TAZs). Parking pricing surveys can also provide a more sophisticated understanding of the price elasticities of parking costs that greatly affect mode choice and consequently, travel behavior.

Parking surveys conducted to improve the travel modeling process are similar to workplace and establishment surveys (see Chapter 10.0), in that trip-makers are usually surveyed at the attraction end of their trip. The purpose of collecting these data relates to the number, type, and geo­graphical distribution of the trips attracted to a specific facility within the framework of the travel model. Workplace and establishment surveys are more common, and, in many cases, may prove to be more effective in gathering travel behavior data than parking surveys. An important con­sideration related to the implementation of parking surveys is that, by definition, the data may be biased since only information about the auto­mobile travel mode is collected.

Survey teams should consider using the parking survey instead of the workplace and establishment survey (or as a supplement to either) for input into the travel modeling process:

• To obtain data about specific parking facility (lots and garages) loca­tions;

• To obtain accurate parking facility cost data;

• To obtain trip origin and destination data on automobile users who may park in a central location while traveling to their actual destina­tions by other modes such as walking and public transportation (e.g., shoppers and workers in a Central Business District);

• To obtain auto, transit, and walk access information for trip makers traveling from parking facilities to their actual destinations;

• To obtain information on the short-term and long-term parking facility mix;

• To obtain detailed information for specific subareas within the travel modeling system; and

• To obtain data on trip making to and from park-and-ride facilities if new infrastructure improvements are being considered.

• A special consideration is “parking congestion”, an analog to roadway congestion. Data on when parking lots reach capacity and how that alters travel behavior is an important component of any fine-grained facility analysis.

The following types of parking facilities should be targeted for surveying in order to collect travel behavior information for input into the travel modeling process:

1. Parking garages or lots available to the general public. If a facility serves only one employer or one building, a workplace/establishment survey will likely result in a higher response rate at lower survey im­plementation costs. Also, if a particular parking facility is only open to specific parkers such as parkers with monthly passes, parking sur­veys will probably not be an effective means of gathering unbiased travel behavior data.

2. Parking garages or lots available to the general public that cater to non-work users such as shoppers and tourists. These types of activi­ties are less predictable than work travel, and therefore parking sur­veys may provide additional input and detail about overall travel behavior.

12.1 Assembly of Background Data

The survey team should first develop an accurate database on the parking inventory of the particular area of study. Similar to the workplace and establishment surveys, key information to gather includes the number of available spaces by parking facility; specific locations of the parking facili­ties (considering both the existing roadway system and travel model transportation network system); specific driveway locations; parking facil­ity access, egress, and proximity to the existing transit and highway sys­tems; parking facility characteristics such as capacity, square footage, type (surface or garage; passenger car, commercial vehicle, handicap, bus, etc.); various pricing rates and mechanisms; short-term and long-term parking mix; and if available, average parking facility usage and turnover rates.

Typical sources used to develop the parking inventory include:

• Direct interviews with privately owned parking facility management companies;

• Detailed roadway maps (such as Sanborn Maps) and travel model transportation network maps/plots;

• Public Works Departments/Departments of Transportation parking in­ventories; and

• Assessors Department inventories.

Information collected from the sources mentioned above may not be com­prehensive and may be difficult to collect. For example, privately owned parking management companies may not be amenable to sharing infor­mation about their parking facility characteristics. Therefore, additional information can also be collected by conducting field visits of the parking facilities in order to gather comprehensive parking inventory data. Field visits typically take the form of windshield surveys designed to identify rate structures, facility types, driveway locations, access and egress to transportation systems, usage, and other key parking facility characteris­tics. Data on facility usage and turnover can be treated as part of the survey design rather than as background data if it is not available from the facility manager.

12.2 Designing and Organizing Parking Surveys

Parking survey design methods include:

• Interviewing automobile parkers arriving and/or leaving a parking facility;

• Providing mail-back questionnaires on the windshields of automobiles parked in the facility; or

• Recording license plates of parked cars, obtaining respondent addresses from DMV files and mailing them a survey.

• Timed counts of facility usage relative to capacity.

Mail-back surveys are typically less labor intensive and costly than the in­terview survey and tend to be easier to administer. However, mail-back surveys typically obtain lower response rates and require a large distribution of survey forms to achieve the required survey sample. The license plate approach, which can employ either mail-back or interview surveys, is very similar to the license plate methods de­scribed in Chapter 7.0, and therefore is not detailed in this chapter.

With interview surveys, it will be necessary to determine the appropriate sampling procedure (see Chapter 5.0 and the sampling section of this chapter) and interview schedule. For example, should interviews be con­ducted for arriving or departing motorists from the parking facility. The advantage of conducting interviews upon departure is that the motorist can report the actual duration and price incurred for the particular sur­veyed trip.

With mail-back surveys, all parkers should receive a survey form. At parking garages or attended parking lots, survey forms can be handed out as parkers enter the facility. At unattended lots or on-street parking spaces, surveyor schedules must be established to determine how often it will be required to distribute survey forms on newly parked cars. At locations that serve mostly commuter parking, a morning distribution of survey forms is typi­cally distributed. However, at parking facilities that cater to a wide range of parkers (such as shoppers, tourists, office workers) and include high parking turn-over rates, frequent survey form distribution may be re­quired.

12.3 Sampling

If the interview approach is used to conduct the survey at unattended lots and/or on-street parking spaces, it will be necessary to identify a sample of specific parking spaces to conduct interviews.As with any sampling plan, sample parking space selection should relate parking space universe, sampling frame, and desired levels of confidence and precision - and special methods of sample selection (e.g., stratification) as circumstances require. The sample should take into account that turnover and rate of utilization is spatially distributed, especially in larger lots which fill more slowly on their periphery.

Each motorist parking in the identified sample of parking spaces will then be approached by the surveyor for potential interviewing. This method will produce a random sampling similar to interviewing each member of a household using ran­domly selected telephone numbers in the household travel interview sur­vey.

In order to determine the number of interviewers required to conduct a parking survey, the proportion of short-term versus long-term parkers must be determined. The information obtained in the parking inventory, will provide key data regarding the parking mix to develop the sampling plan for the survey. At garages and attended parking lots, interviews can be carried out at facility driveway entrance and/or exit locations.

If the mail-back survey is used, the parking inventory database will also provide key data regarding the usage, mix, turnover, and number of automobiles using the parking facility being surveyed. This information will be used to identify the survey form printing requirements to ensure that each vehicle parked in the facility will be surveyed. Since the re­sponse rate (number of usable survey forms versus the number of sur­vey forms distributed) for mail-back surveys are typically low, survey forms should be handed out to each motorist (or placed on each automo­bile) to increase the likelihood of obtaining fully completed surveys. The inven­tory will provide information necessary to determine how frequently fieldworkers will need to go to unmanned and metered parking locations.

12.4 Drafting and Constructing Survey Instruments and Materials

Depending on the survey approach taken, the survey instrument should be constructed to be usable in the field and to elicit the appropriate motor­ist responses to obtain required data for input into the travel demand modeling process. This includes drafting the appropriate questions to meet the needs of the travel model. The interview and mail-back surveys are typically constructed differently. For example, interview survey ques­tionnaires are designed to allow quick and easy interviewer tallying of motorists responses by using personal interview scripts and CATI pro­grams. On the other hand, the mail-back survey questionnaires because they are self-administered, must be clear and easy for the respondents to fill out. Furthermore, if the survey form is designed to be scannable, spacing of the questions is important to ensure that all necessary data elements are obtained.

The construction of the questionnaire typically follows similar procedures as used for other types of surveys including the vehicle intercept and ex­ternal station surveys (see Chapter 7.0) and workplace and establish­ment surveys (see Chapter 10.0). Guidelines for constructing mail-back or self-administered questionnaires described in previous chapters should be followed for the parking survey.

If the parking survey is going to rely on distributing self-administered forms on parked vehicles’ windshields, the forms need to be designed to stand up to the elements to some extent (surveys of this type should not be conducted in very bad weather). In addition, the forms should be made to be as visible as possible so that motorists see them before they get in their vehicles.

Questions that typically appear on parking survey questionnaires include:

• Purpose of the trip;

• Ultimate (actual) as well as parking facility origin and destination in­formation;

• Location of the residence of the parker (when trip is non-home-based);

• Arrival and departure time to/from the parking facility;

• Perception of the difficulty of finding parking;

• Strategies used to park at preferred locations;

• Frequency (average weekly and monthly frequency) of parking at sur­vey location;

• Payment information (form of payment, short-term and long-term costs, etc.);

• Auto occupancy;

• Demographic information about the parker (including income);

• Walking distance/time from parking facility to actual destination; and

• Location and land use of actual destination.

12.5 Pretesting

As with any survey, pretesting should be carried out prior to implement­ing and administering the survey. For both interviews and mail-back sur­veys, it is important for the survey team to test the entire process to ensure each component of the survey is feasible and obtains the appropriate level of information required for analysis and travel modeling purposes.

In some cases, mail-back survey pretesting can be administered on a small scale to persons within your company/agency to identify inconsistencies and other issues associated with the format and wording of the question­naire. See previous chapters of this manual for more detailed procedures and requirements for pretesting.

12.6 Training and Interviewing Fieldworkers

Similar methods for survey training described in other chapters of this manual should be used to train and brief the parking survey fieldwork staff. For example, the training methods described for the vehicle inter­cept and external station survey and in particular the Roadside Interview Survey can be used for the interview parking survey described in this chapter. In addition, the training methods for the Roadside Handout Survey described in Chapter 7.0 are very similar to parking mail-back survey also described in this chapter.

In most cases, survey training is conducted prior to the pretest and im­plementation of the overall survey with all participating surveyors and in­terviewers. This session is typically conducted several days before the scheduled pretest and overall survey dates. Similar to other surveys de­scribed in this manual, surveyors are briefed on the purpose and proce­dures on how to conduct the survey. Items generally covered by survey team include:

• Project Briefing describing the background and purpose of the survey and a description of survey assignments for all surveyors;

• Survey demonstrations on the procedures of the survey administration describing surveyor/interviewer responsibilities for distributing ques­tionnaires and/or interviewing motorists, survey schedules, etc.; and

• Survey procedures checklist provided to the surveyors and/or inter­viewers during the initial briefing session including authorization let­ters and background material.

As part of this process, it is important for the survey team to coordinate with the fieldworkers to ensure that they have been distributed all of the necessary survey materials required to successfully carry out the survey. In the case of the parking survey, the survey materials and instructions for the mail-back and interview surveys differ because of the method for con­ducting the survey. Similar to specifications described in Chapter 7.0 for the vehicle intercept and external station survey, these materials include:

• Survey forms (interview format and mail-back format as appropriate);

• Record keeping forms;

• Clipboard (for interviewers);

• Writing instruments (preferably pencils); and

• An authorization letter describing the intent of the survey and the request for survey participation.

In the case of the mail-back survey, the survey team must provide addi­tional instructions to the surveyors placing questionnaires on parked automobiles. Fieldworkers should be provided with instructions describ­ing procedures related to the possibility of parkers approaching them or the possibility of parkers remaining in their vehicle during the distribution of the survey questionnaires. Fieldworkers need to know how often they should distribute the survey questionnaires and what area they are ex­pected to cover in the distribution. If the survey questionnaires have serial numbers, fieldworkers will be able to track the parking facility loca­tions and times of survey distribution. If fieldworkers are distributing ques­tionnaires in a staffed garage or parking lot, they must notify the garage attendant before starting to distribute the questionnaires. The sur­vey administrator should discuss details of survey form distribution including:

• If a questionnaire is on a windshield already, there is no need to leave additional questionnaires during subsequent distributions;

• Place the survey questionnaire on the driver’s side of the windshield;

• For the on-street survey, make sure to put survey questionnaires on car windshields on both sides of the street;

• Be careful not to damage the windshield wiper or any other part of the car when distributing the survey questionnaire; and

• Survey questionnaires should be placed so that the official logo of the project and sponsoring agency is readily visible to the parker.

Similar interviewing techniques identified for the Roadside Interview Survey described in Chapter 7.0 should be used by interviewers to con­duct the parking interview survey. The following instructions should be followed if the parking interview survey is conducted:

• If applicable, setup the survey station near parking facility entrance and exit driveways/booths in order to warn motorists of the survey;

• Describe the survey to solicit driver participation;

• If motorists refuse to participate, politely thank them for their time and wait for (or move on to) the next motorist;

• Record all collected information neatly and accurately on the question­naires; and

• Organize the collected questionnaires by parking facility location and time period.

Variations of interviewing procedures can be used depending on the sur­vey method used and parking facility to be surveyed. For example, the survey station setup will not be an appropriate step for the interviewer if motorists using on-street parking spaces are surveyed. Also, the survey station setup at a staffed parking garage may include a notice warning motorists of the survey schedule at the entrance/exit booth.

12.7 Coding

Parking survey coding is conducted using similar procedures used for other surveys described in this manual. In the case of the parking survey, similar techniques are used to code the mail-back and interview surveys. The survey questionnaires are typically designed to be self-coding (except for the origin-destination information), where each survey response can be coded to correspond to its answer check box number. Data coding can either be completed by hand by the surveyors conducting the interview survey and motorists completing the self-administered mail-back survey, or by CAPI for surveyors conducting the interview survey.

Since Parking as travel behavior, sui generis, has not been surveyed extensively, pre-testing questions about parking strategies and other parking behavior may be required. These will, necessarily, not be self-coding in their original form.

The survey data are typically punched into a numerical ASCII database for a specified width and length as determined by the number of ques­tions/responses and sample size of the survey. Individual survey ques­tionnaire responses are typically given an identification number to track the responses for each parker surveyed. Survey origins and destinations must be geocoded to identify the geographic locations of the parkers sur­veyed. Chapter 14.0 provides a detailed discussion of survey geocoding techniques.

12.8 Cleaning and Editing

Similar data cleaning and editing techniques used for other surveys de­scribed in this manual are also conducted for the parking survey. As stated in previous chapters, completed questionnaires should be edited as soon after collection as possible to ensure that the proper surveyor tech­niques have been used and the appropriate information has been obtained. Range checks should be conducted to identify any data inconsistencies that may occur in the coding process and to verify the accuracy of the data.