Research Note 96-11: Driving Patterns and Emissions: A New Testing Cycle

 

ARB logo

 California Environmental Protection Agency

Air Resources Board

 No. 96-11

December 1996

 RESEARCH NOTES

Brief Reports to the Scientific and Technical Community


 Research Division, John R. Holmes, Ph.D., Chief

P.O. Box 2815, Sacramento CA 98512

 

 Driving Patterns and Emissions: A New Testing Cycle

 A new speed-versus-time vehicle emissions modeling driving cycle for light- and medium-duty vehicles was developed that more accurately reflects real-world driving patterns than does the current standard test cycle, the Federal Test Procedure (FTP). Emissions of carbon monoxide and oxides of nitrogen resulting from the new driving cycle were found to be higher than those produced during the FTP. This project was carried out by Sierra Research, Inc.

Background:

Methods:

Results:

Significance and Application:

Related Projects:

Since the late 1980s efforts have been expended by researchers in government, industry, and the academic community to more accurately quantify emissions from motor vehicles. Because the standard driving cycle test, the Federal Test Procedure (FTP), does not well represent real-world driving behavior, this study was conducted to develop a new speed-versus-time vehicle emissions modeling driving cycle that would do so.

A chase car followed light-duty vehicles over 102 different routes in the South Coast Air Basin. The routes were selected using data from the Southern California Association of Governments' Urban Transportation Planning System model. Uniform distance was maintained between the chase car and the subject car with a range finder laser developed for this study. The chase car collected data on chase car speed, manifold air pressure, and acceleration, subject vehicle speed and range, and other parameters. The data were broken into 833 microtrips (a microtrip is the portion of travel that occurs between stops) and assembled into a driving cycle (the "LA-92") representative of real-world trips of about 20 minutes' duration.

In addition, beginning with a model originally developed by the Department of Transportation, the contractor developed a pair of computer models for estimating second-by-second emissions and used these models to compare exhaust emissions from a typical vehicle as estimated by the LA-92 and the FTP.

The driving cycle developed in this study is designed to be more representative of all the modes of vehicle operation (hard accelerations, etc.) than is the FTP. Compared to the FTP, the LA-92 cycle has a higher top speed (67.0 mph versus 56.7 mph), a higher average speed (24.8 mph versus 19.6 mph), less idle time (16.4 percent versus 19.0 percent), fewer stops per mile (1.52 versus 2.41), and a higher maximum rate of acceleration (3.02 m/sē versus 1.48 m/sē ). The LA-92 is 9.9 miles long; the FTP's length is 7.5 miles.

One of the models developed for this study, the VEHSIM (vehicle simulation), uses a specified input driving schedule to produce a set of second-by-second engine state estimates (e.g., engine speed and load). These estimates are then used as input to the other model, VEHSIME (vehicle simulation emissions), to estimate second-by-second emissions for that driving schedule. Used to compare the LA-92 with the FTP, these models projected emissions of carbon monoxide and oxides of nitrogen to be over twice as high for the LA-92. Hydrocarbon emissions were about the same for both cycles.

Mobile sources have been identified as major contributors to California's air quality problems, and a number of mobile-source-related measures are contained in California's State Implementation Plan for Ozone, aimed at attaining the Federal ozone standard. Thus, it is important that there be accurate emissions inventories for mobile sources, especially for light-duty vehicles, which constitute the greater proportion of California's on-road vehicles. The LA-92 cycle was developed as an emissions inventory improvement tool, and it is expected to play a major role in current and future emissions inventory improvement efforts.

The LA-92 has been used to develop a cycle correction factor for the ARB's on-road motor vehicle emissions factor model EMFAC7G. (Emissions factors are average values that relate the quantity of a pollutant emitted to the atmosphere with the activity associated with the release of that pollutant. )

The ARB has sponsored three other studies to measure driving behavior. The first two projects studied light-duty vehicles; the third project analyzed heavy-duty trucks. These studies were (ARB contract number is in parentheses): On-Road Motor Vehicle Activity (A-132-182), Monitoring of Personal Driving Habits and Vehicle Activity (A132-175), and Heavy-Duty Truck Population, Activity and Usage Patterns (93-306).

 This research was conducted under contract with Sierra Research, Inc. (ARB Contract No. A932-185). Comments or questions can be directed to the contract manager, Hector Maldonado, by mail, FAX (916) 322-4357, phone (916) 323-1508, or e-mail: hmaldona@arb.ca.gov. For an index of Research Notes, call (916) 445-0753 or FAX (916) 322-4357.

 Copies of the research report upon which this Note is based can be ordered from:

National Technical Information Service
5285 Port Royal Rd
Springfield VA 22161
Request NTIS No. PB94-157005

 Title: Characterization of Driving Patterns and Emissions from Light-Duty Vehicles in California

 Author(s): Thomas Austin, Francis DiGenova, Thomas Carlson, Richard W. Joy, Kathyrn A. Gianolini, John M. Lee