Department Overview  

Copyright © 2001
Department of Transportation Studies
Texas Southern University

Collection and Evaluation of Modal Traffic Data for Determination of Vehicle Emission Rates Under Certain Driving Conditions

Principal Investigator:    Dr. Lei Yu

Sponsoring Agency:    Texas Department of Transportation and Federal Highway Administration

Research Objectives:

The primary objectives of this research are to use a RES to collect on-road emission data, evaluate various existing emission estimation models with on-road emissions, and develop an emission estimation model that can be used to evaluate emission implications of alternative traffic control and management strategies. The emission data collection uses the Smog Dog (SBRC, 1995), a RES which was developed by the Santa Barbara Research Center (SBRC), which is an application of space technology in vehicle emission sensing. The Smog Dog can collect the emission concentrations of CO, HC, and NOx. It can also simultaneously record a vehicle’s instantaneous speed value and acceleration/deceleration rates while its emission is detected. The new developed emission model will establish relationships between the on-road vehicle exhaust emissions and a vehicle’s instantaneous speed and acceleration rate. This emission model can be used to evaluate emission implications of alternative traffic control and management strategies.

Data Collection Equipment - Remote Emission Sensor

The RES that is used in the vehicle emission data collection is called SMOG DOG (SBRC, 1995 and Jack et al, 1995), which was developed by the Santa Barbara Research Center (SBRC), a wholly owned subsidiary of Hughes Aircraft Company. It is an application of advanced technology developed for environmental monitoring from space to accurate measurement of automotive emissions on earth. It was initially developed for providing a cost-effective tool for screening for high emitter vehicles and has experienced many successful applications in Arizona, California, North Carolina, Alaska, Georgia, and New Mexico. Some other states are also starting the use of RES to reduce automobile pollution.

The SMOG DOG, which consists of a sensor head, source, video camera, and state-of-the-art electronics for capture, display, and storage of both image data (automobile license plates) and vehicle emission data, uses a remote sensing technique that has been used for many years for satellite monitoring of ecological and environmental points of interest like earth’s atmosphere and forest. In its vehicle emission sensing, infrared “light” is passed through a vehicle’s exhaust plume and is absorbed by the different gases in the plume. The sensor determines changes in the selective absorption of infrared radiation by molecular vibrational modes at wavelengths specific to the pollutant; i.e., HC, CO, NOx, and CO₂. Changes are measured using chemically specific detectors, which sense radiation only at these wavelengths. The motion of a vehicle through the beam triggers the simultaneous measurement of CO, HC, NOx, and CO₂ in the dispersing exhaust cloud for a user-selectable period (typically one-second). The data from all four pollutants are analyzed in a real time and the results, expressed as a percentage of the exhaust, are stored on computer disk. The image data is stored on a VCR tape, which can be read by an operator and the license plate information is entered into the same file as the emission data

Data Collection Sites

Research Abstract

This report presents a research effort for collecting the on-road vehicle emission data, developing the ONROAD emission estimation model and evaluating existing emission estimation models including the emission factor models MOBILE and EMFAC. The on-road emission data were collected from five highway locations in Houston using a Remote Emission Sensor (RES) called Smog Dog, which was developed by the Santa Barbara Research Center (SBRC). The Smog Dog is used to collect the emission concentrations of CO, HC, and NOx, as well as to simultaneously record a vehicle’s instantaneous speed value and acceleration/deceleration rates while its emission is detected. During the emission data collection, the ambient temperature and humidity were periodically recorded. The collected emission data are used to develop the ONROAD emission estimation model, which consists of a series of emission estimation equations. In these emission estimation equations, the emission rates are made functions of a vehicle’s instantaneous speed, acceleration/deceleration rate, ambient temperature and humidity. It can be used to estimate the emission reductions that may be obtained through the operational improvements of traffic control and management strategies. The emission factors that are derived from MOBILE and EMFAC are compared with the collected on-road emission data by emulating the standard FTP driving cycles using the ONROAD emission rates. In general, both MOBILE and EMFAC are found to underestimate on-road vehicle emissions. However, these two models are the only EPA approved models for establishing mobile source emission inventories. Efforts are also made to compare the emission estimations in traffic simulation models with the on-road emission data. It is found that traffic simulation models considerably underestimate the on-road emissions, and thus these models are not recommended for use in performing any field vehicle emission analysis.

Research Reports

Three volumes of the research reports have been published by Department of Transportation with Report No. TxDOT 1485-1, TxDOT 1485-2, and TxDOT 1485-3F.  The research was also presented at TRB 1999 Annual Meeting (99-0081) and published in Journal of Transportation Research Part D: Transport and Environment, Vol.3, No. 5, pp. 337-347.  To order a copy of reports, please contact Dr. Lei Yu by telephone at (713) 313-7282 or by e-mail at yu_lx@tsu.edu.