Vehicle Occupancy Data Collection Methods
Traditionally, vehicle occupancy rates are used to convert person trips to vehicle trips in the four-step travel demand forecasting process and to determine the required parking spaces for fixed-seat facilities such as sporting facilities and performing centers. The Intermodal Surface Transportation Efficiency Act (ISTEA) of 1991 expanded this traditional role of vehicle occupancy rates by requiring continued monitoring of congestion management strategies, many of which emphasize person movement rather than vehicle movement. Today, traffic engineers use vehicle occupancy data to compute person delays; transportation planners use vehicle occupancy rates to derive person-miles traveled and to set policies for managed lanes; transit planners use transit occupancy rates to identify routes that need service expansion; etc. More applications of vehicle occupancy data can be expected. For example, transit advocates are proposing person volumes as the basis for traffic signal warrants, transit signal priority, and transit preferential lanes.
With this increasing need for vehicle occupancy data comes the need to examine and reexamine the ways in which these data have been, and will be, collected. Unlike counting vehicles, which can be automatically recorded when vehicles run over pneumatic road tubes, counting the number of persons in a vehicle in the field remains the task of human observers. In the face of budget reductions, agencies must find better ways and define acceptable practices of collecting vehicle occupancy data that not only meet the needed accuracy, but also meet the limits of a restricted budget.
Only a very limited number of studies have examined methods and issues related to collection of vehicle occupancy data. The most comprehensive study to date has been performed by Heidtman et al. (1997) for the Federal Highway Administration. The study evaluated various data collection methods with field data and provided relatively detailed comparisons of the mtehods. In Florida, the Florida Department of Transportation (FDOT) undertook a statewide pilot study in 1996 and 1997 to examine alternative methods of data collection, observation locations, field procedures, treatments of commercial vehicles, etc. (Liu and Desai 1998; Reed et al. 1998). As part of the study, over 2,000 hours of vehicle occupancy data from 21 sites covering different types of roadways throughout the state were collected.
While these studies have been relatively comprehensive, much remain to be done. No formal guidelines have been developed to assist users in selecting the proper methods and the associated geographic, temporal, and vehicle coverage for specific applications. In addition, it is necessary to explore the use of new technology to improve existing methods, to investigate alternative methods, and to develop tools that can ease data collection, processing, and analysis.
This project aims to:
- Research and evaluate existing methods of vehicle occupancy data collection with respect to their geographic, temporal, and vehicle coverage design.
- Identify new methods and study their feasibility as a potential source of vehicle occupancy data.
- Recommend acceptable practices for various methods and issues related to vehicle occupancy data collection.
- Present recommended practices as Florida’s guidelines for the collection of vehicle occupancy data.
- Develop tools to facilitate the collection, processing, and analysis of vehicle occupancy data.