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Project at a Glance

Title: Determination of non-registration rates for on-road vehicles in California.

Principal Investigator / Author(s): Durbin, Thomas

Contractor: UC Riverside

Contract Number: 99-318

Research Program Area: Emissions Monitoring & Control

Topic Areas: Mobile Sources & Fuels


The College of Engineering, Center for Environmental Research and Technology (CE-CERT) has completed a statewide survey of vehicle registration in California. This work was conducted under a contract from the California Air Resources Board (CARB). The on-road vehicle fleet in California is composed of California registered vehicles, unregistered vehicles, and out-of-state vehicles. Obtaining accurate emissions estimates for all on-road vehicles requires an understanding of the percentage in each group as well as the types of vehicles in each group. The percent of unregistered vehicles on the road throughout the state is an important and largely unknown quantity.

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. It is believed that these enw measures have led to increases in the number of unregistered vehicles in the state especially poorly maintained vehicles that can not 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 CARB.

The objectives of this CARB-sponsored project were to determine the portion of in-use vehicles in California that are unregistered and to assess the number of out of state and out of country vehicles in use in California. With this information, CARB 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 random locations in every county in the state and encompassing more than 98,000 identified vehicles. Data collection occurred between June 2000 and December 2000. The observed vehicle registration information was correlated with BAR Smog Check results as well as DMV registration information. Vehicle information was obtained through VIN decoding to provide information on the specific characteristics of the identified vehicles. The results of this study are detailed in this report.


For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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