Wall Street Journal writer Carl Bialik tackles the science behind traffic.
Mathematicians, engineers and planners are making steady advances in assessing traffic congestion and explaining it. Radar and GPS devices help pinpoint cars and relay traffic data in real time. And sophisticated models can explain maddening phenomena such as phantom jams, when cars slow even without congestion. But traffic math’s strides in reducing congestion are modest, simply because the number of cars often exceeds roadway capacity.
What works?
David Schrank, co-author of the institute’s Urban Mobility Study, says things would be even worse without creative, data-driven measures to manage traffic, such as ramp metering, which controls the flow of vehicles onto highways. But these tools don’t make a huge difference: They shaved an average of about three minutes of travel time for each rush-hour commuter, each week.
This still might be a better track record than the alternative approach of adding roads, which traffic engineers say often have only a fleeting impact on easing congestion. Instead, new roads lead to more travel, because of an effect that Martin Wachs, director of RAND Corp.’s transportation, space, and technology program, describes as triple convergence. Many drivers who had shifted their trips to off-peak hours, or to different roads, or to public transit, resume their previous pattern and converge onto the new highway.
Rather than plan new roads, most traffic engineers are working to spread traffic out more evenly.
Photo Credit: AP Photo/Jacquelyn Martin
I’m writing scientific work about traffic congestion and would like to add that GPS can help us avoid roadways that exceeds capacity.