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Center for Transportation Studies

Ramp Meters on Trial

Presentation by Dr. David Levinson, Department of Civil Engineering

September 10, 2002

The Intelligent Transportation Institute's seminar series kicked off the semester with a presentation by David Levinson, assistant professor of civil engineering, on a subject that has been on the minds of researchers and legislators in Minnesota for quite some time.

Levinson has been studying the effects of freeway ramp meters in the Twin Cities for several years. His seminar presentation, titled “Ramp Meters on Trial,” examined the original intentions of the traffic professionals who began installing ramp meters around the metropolitan area over two decades ago, as well as the good and bad consequences of ramp metering in the present day.

The original purpose of ramp metering in the Twin Cities, Levinson explained, was to maximize the freeway system's overall efficiency — defined as the ability to move more vehicles through any given stretch of freeway in a given time interval. To accomplish this, delays would be imposed on cars waiting to enter the freeway, in order to guarantee a smooth, fast traffic flow on the main roadway. But an ever-increasing metropolitan population, coupled with a lack of funding for expanding freeway capacity, led to increasing delays at ramp meters — until drivers' annoyance outweighed the perceived benefits of fewer delays on the freeway itself.

Levinson's research is currently focused on the problem of how to distribute delays more equitably among all drivers, so that drivers waiting to enter the freeway are not unfairly penalized for delays occurring elsewhere in the system. He is attempting to develop a functional measure of efficiency and equity for ramp metering, drawing from such diverse fields as engineering, economics, and land use planning. But integrating these disparate fields' widely varying measures of "what's good" is an engineering challenge in itself.

One of the main issues explored in Levinson's research into the equity of ramp metering is how delay caused by ramp meters is distributed among highway users. Adding analytical tools originally developed by economists studying income distribution to the research methods of civil engineering, Levinson is exploring tradeoffs between equity and efficiency.

Another area of interest is the effect of ramp meters on travel time variability. Previous research has established that ramp metering makes travel times more consistent – a definite advantage for commuters planning to be at work on time. New methods to maximize this benefit while minimizing inequity among drivers may emerge from this project and be incorporated into future ramp meter control systems.

With traffic in the Twin Cities area unlikely to decrease in coming years, the work of Levinson and other researchers on ramp metering will be sure to find a place in Minnesota's transportation equation.