Doctoral Dissertations

Date of Award

5-1997

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Civil Engineering

Major Professor

Arun Chatterjee

Committee Members

Fred Wegmann, Terry Miller, Elden DePorter

Abstract

Following the passage of the Clean Air Act Amendment (CAAA) in 1990, there have been renewed efforts to accurately quantify the emission of pollutants from mobile sources. There are two existing approaches to estimate exhaust emission from mobile sources: 1) MOBILESa, which was the "Average Speed" approach and, 2) TRAF-NETSIM, which was the "Modal" approach. This study identified the strengths and limitations of these two approaches for vehicle exhaust emission estimation. To make a valid comparison between the two approaches, the hot- stabilized portion (Bag 2) of the FTP cycle was used as a common platform to calibrate the two independent approaches. Using the results of traffic simulation, the difference between these two approaches was quantified. The base line comparison of average emission rates from a modal approach and an average speed approach produced interesting results. It was observed that the average emission rates for all three pollutants (HC, CO, NOx) reported by MOBILESa were greater than the average emission rates obtained from TRAF-NETSIM embedded tables. Within the operating range of FTP hot stabilized portion, emission rates for HC, and CO obtained from MOBILESa were three times higher than that obtained from modal approach. However, for NOx, MOBILESa's rates were one and half times higher than those of TRAF-NETSIM. This study developed modal adjustment factors (MAFs) for each pollutant, which was defined as the ratio of the actual emission rate embedded in NETSIM for a specified combination of acceleration and speed to the average FTP emission rate of the pollutant. This study illustrates that MAFs vary widely — from 0.3 to more than 150 times — implying that the average FTP emission rates are not truly representative of modal rates within the considered ranges of speed and acceleration. This study demonstrated the use of both "modal" and "average speed" approaches for the evaluation of the impact of a traffic improvement strategy on emissions from light duty gasoline vehicles. The traffic improvement strategy that was analyzed was the coordination of traffic signal operation along an arterial road. A simple case involving an arterial operation was selected to achieve this objective. The analysis was performed using TRAF-NETSIM for the modal approach and MOBILESa was used for the average speed approach. The reduction in the cumulative hourly emission for all three pollutants (HC, CO, and NOx) due to the implementation of signal coordination using the modal approach was larger than those of the average speed approach. The average speed approach reported a negative benefit (an increase) for NOx due to signal coordination. This study used a simulation-based procedure for quantifying the effect of driver behavior on mobile source emissions. Two mixes of driver populations were examined: uniform and aggressive. It was found that the quantity of emissions considerably increased with the increase in the aggressiveness of driver population. Based on this study, it was concluded that the base emission factors used in various analytical models may be corrected for aggressiveness of driver population. This study was limited to nonfreeway arterial operations only. Because freeway operation is different with respect to acceleration and speed, a similar analysis should be performed to evaluate freeway operation to gain a more comprehensive understanding of the characteristics of modal emissions.

Download
Files over 3MB may be slow to open. For best results, right-click and select "save as..."

Share

COinS