Debunking Road Widening Myths #3 - More Capacity Means Relief vs. Build It and They Will Come

Induced Demand - the phenomenon that after supply increases, more of a good is consumed.

In the first part of our Debunking Road Widening Myths series, we cited a quote from Forsyth County consultants Kimley-Horn that stated road widening does not alleviate traffic congestion because the increased capacity simply results in more cars traveling more miles.  On what basis do they make that claim, and would increasing capacity across a broader network solve the problem?  California's DOT admits that more roads mean more traffic.

Further, a study by Susan Handy of the Department of Environmental Science and Policy at the University of California, Davis documents the effects of road widening and capacity increases, and concludes that Induced Demand does indeed exist.

Wes Marshall is co-author of "Elements of Access: Transportation Planning for Engineers, Transportation Engineering for Planners".  He provides this simple diagram to explain the actual effects of roadway capacity increases:

Induced Demand.jpg

There is a wealth of documented study confirming that road widening and capacity increases actually results even more traffic volume and ongoing congestion.  We need only look at our own roads that have been widened over time - has our traffic congestion situation gotten any better, or has it increased?  An objective review of the evidence would suggest that it has simply supported additional area growth and density that ultimately combined to outpace that capacity that was added.  Doing so again won't solve our problem in the long run - it will simply make it an even larger problem in the future.

With the upcoming approval of our updated Comprehensive Land Use Plan on the horizon, we would be better served by seriously considering the correlation between ongoing development, density, and traffic congestion.  Road widening and capacity increases are the short-sighted solution that seeks to treat the effect instead of the cause.