Energy and Air Quality Benefits of Freeway Bottleneck Improvements
Carol H. Walters, Mark D. Middleton and Poonam B. Wiles, Texas A&M University, August 1996, 51 pp. (60039-1)
Freeway bottlenecks cause deterioration in freeway operation. These overcapacity sections of freeway are responsible for increased fuel consumption, increased emissions, and increased delay to motorists. The Texas Department of Transportation has funded and implemented many freeway bottleneck improvement projects around the state to reduce these problems. These projects provide significant benefits in terms of increasing speeds and reducing delays; however, little information exists on quantifying energy and air quality benefits from implementation of bottleneck removal projects.
This research investigated the relationships between traffic operating characteristics and environmental factors such as fuel consumption, hydrocarbon emissions, carbon monoxide emissions, and nitrogen oxide emissions. A methodology was developed to analyze existing before and after data from traffic improvement projects that have been implemented. The change in fuel consumption was quantified and guidelines were developed to help predict energy benefits from implementing future bottleneck improvements. The total reduction in fuel usage ranged from 0.0% to 5.2% for the examples studied, with an average of 2.2%.
However, the attempt to quantify the air quality benefits was less successful and further research, now underway on a national level, will be required. Current methodology is based on an average speed, and this fails to account for the stop and go nature of driving within congestion upstream of a bottleneck. Under such conditions it has been demonstrated that greater emissions occur, but this has not yet been reliably quantified.
Keywords: Fuel Consumption, Vehicle Emissions
SUMMARY REPORT (Adobe Acrobat File – 4.7 MB)