Research Projects

Project at a Glance

Title: On-road motor vehicle activity data

Principal Investigator / Author(s): Horie, Yuji

Contractor: Valley Research Corporation

Contract Number: a132-182

Research Program Area: Emissions Monitoring & Control

Topic Areas: Behavioral Change, Mobile Sources & Fuels


The objectives of this study were threefold: (1) to develop county-specific estimates of the transit bus fleet and vehicle miles of travel (VMT) ; (2) to develop county-specific estimates of the school bus fleet and VMT; and (3) to determine representative driving patterns of transit buses and school buses. For transit buses, the fleet and activity data compiled by the Federal Transit Administration (FT A) and the American Public Transit Association (APT A) were obtained and analyzed. A supplemental manufacturer survey was conducted to obtain bus specification data, which were then used to develop a regression relationship between bus length and gross vehicle weight for buses listed in the FTA and APT A databases. In the base year of 1990, 8,631 active transit buses were operated in the state and were driven 311 million miles or 36,000 mi/y per vehicle. These statewide fleet and VMT figures were then allocated to each ARB weight class and each county using the regression relationship and county allocation scheme developed under this study. For school buses, the California Highway Patrol (CHP) conducts an annual safety survey on every carrier or terminal in the state. Summary statistics of this bus safety inspection data were found to be the most complete and useful data source for estimating school bus population and annual VMT. To supplement the CHP school bus data, a public school survey for all school districts and a contractor survey for eight major school bus contractors were conducted. Results of the two surveys provided general usage pattern data and detailed fleet characterization data such as model year, bus length, and annual mileage accumulation rate. These survey results and U.S. Census student enrollment statistics were used to develop a methodology for disaggregating the CHP school bus data into each ARB weight class and fuel type, and to each county. Statewide, 23,900 school buses were operated and driven 317 million miles or 13,000 mi/y per vehicle. Diesel buses account for a great majority of the statewide bus population (81%) and VMT (840/,,). Finally, driving patters of transit buses and school buses in Southern California were studied by following buses for about 30 minutes each with datalogger;' equipped chase cars. A total of 21O bus routes were followed by chase vehicles to characterize bus driving patterns during weekday peak hours (6-9 AM and 3-6 PM in local prevailing time), weekday off-peak hours, Saturday, and Sunday for transit buses, and for school buses during weekday morning and weekday afternoon. Driving patterns were determined in three area types: urbanized, small urban, and rural. The driving pattern data acquired by the chase car study were analyzed and compared with the driving cycle data used in the Federal Test Procedure (FTP). It was found that transit buses idled more frequently and in longer duration than the FTP cycle. Although 'the overall trip speeds were about the same as the FTP's, their average driving speeds were considerably higher than the FTP: 20.7 mph 'IS 17.9 mph. A large time fraction spent in idling about 300/0 of total trip duration --was common to both transit buses and school buses.


For questions regarding this research project, including available data and progress status, contact: Heather Choi at (916) 322-3893

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