ARB Research Seminar

This page updated June 19, 2013

Overview and Results of a Statewide Survey of Vehicle Registration Status in California

Theodore Younglove, Bourns College of Engineering, Center for Environmental Research and Technology, University of California, Riverside

June 03, 2002
Cal EPA Headquarters, 1001 "I" Street, Sacramento, CA

Also presented in El Monte on June 12, 2002

Research Project


The College of Engineering, Center for Environmental Research and Technology (CE-CERT) has recently completed a statewide survey of vehicle registration in the State of California. This work was conducted under a grant from the Air Resources Board (ARB). The on-road vehicle fleet in California is composed of California registered vehicles, unregistered vehicles, as well as, out-of-state vehicles. Obtaining accurate emissions estimates for all on-road vehicles requires an understanding of the percentage in each group. The percent of unregistered vehicles on the road throughout the state is an important and largely unknown quantity. In addition, it is not known if the proportion of unregistered vehicles varies by region or size of city.

The State of California now requires vehicle owners to show proof of insurance before it will issue or renew a vehicle's registration. Proof of emissions compliance is also required every other year for 1974 and newer vehicles. With these measures in place, it is believed this has led to increases in the number of unregistered vehicles in the state - especially poorly maintained vehicles that cannot pass a smog test. Numerous studies have demonstrated that high emitting vehicles are a significant source of emissions in California. Identifying and either repairing or retiring high emitting vehicles is a high priority for the ARB.

The objectives of this ARB-sponsored project were to determine the portion of in-use vehicles in California that are unregistered and to assess the impact that these vehicles may have on the emissions inventory. With this information, ARB can update emissions inventories and develop regulatory strategies to reduce emissions from this subset of the vehicle population. The non-registration rates were determined using extensive field surveys at various locations in each county in the state and encompassing over 90,000 vehicles with readable plates taken from over 130,000 photographs. These results were also used to determine the number of non-California vehicles and vehicles not native to the county of observation. The results of this study will be reviewed in this presentation.

Speaker Biography

Theodore Younglove is Principal Statistician at the Bourns College of Engineering, Center for Environmental Research and Technology at the University of California, Riverside. Mr. Younglove has over 19 years of experience in statistical analysis of environmental data. In his seven years at CE-CERT, Mr. Younglove has authored seven peer-reviewed publications and 18 presented papers at national and international conferences. In 1999, Mr. Younglove presented a paper on model validation as an invited speaker at the American Statistical Association Special Section on Automobile Emissions Analysis. He received a B.S. degree in Statistics from the University of California, Riverside, in 1979 and a M.S. degree also in Statistics from the University of California, Riverside, in 1982. After graduation, Mr. Younglove worked as a statistician at the Statewide Air Pollution Research Center at the University of California, Riverside. He has more than three dozen research papers in a broad range of environmental topics ranging from statistical analysis of the dynamics of plant ozone exposure to prediction of groundwater contamination by pesticides using soils data. At CE-CERT, Mr. Younglove is working with the Transportation Systems Research group where he is currently Principal Investigator on a U.S. Environmental Protection Agency project modeling automobile emissions using a database methodology developed at CE-CERT.

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