News | October 5, 2015

Word on the Street: More lanes often mean more traffic, not less

Every driver who has ever been stuck in traffic has dreamed of having just one more lane available to allow cars to move around the bottleneck.  

But that dream is an elusive one, and building more lanes often results in the same traffic nightmare. The reason is that travelers who have been avoiding the congestion by not taking discretionary trips, traveling at a different time, or taking a bus or train instead of driving are inclined to drive more when new capacity is available. At the same time, new commuters may be brought into the corridor as highway expansion spurs development in new areas. As a result, adding lanes often only provides temporary relief to traffic congestion due to the additional traffic enticed by the promise of easier travel, a phenomenon known as “induced demand”.

“The bottom line is that we can’t just build our way out of congestion. When you try to do that, what we see over and over is that you spend millions of dollars to end up right back where you started,” said Trip Pollard, leader of SELC’s Land & Communities Program.

Those millions of dollars spent don’t even include the additional, recurring costs to maintain those new lanes that are now added to a transportation department’s budget. Nor do they account for the often significant environmental and community impacts of the expanded infrastructure and the suburban sprawl that often accompanies it.

Planners and decision-makers need to consider induced demand when assessing alternatives for addressing congestion. The Georgia Department of Transportation, for one, has recognized that so much potential demand exists in metro Atlanta that it cannot build uncongested interstate lanes. 

While every traffic situation is unique, there are a host of options other than expansion that can help open clogged thoroughfares. In Atlanta, the DOT has decided to toll all new interstate lanes in an effort to reduce the demand on those new lanes and ensure that, at the very least, the new tolled lanes function during rush hour for those willing to pay the extra fee.  

Charlottesville’s Route 29 Solutions project illustrates another approach. There, local drivers are the primary cause of congestion along the business-lined Route 29, so the state is upgrading the parallel road network to give those drivers alternatives to using the main highway, as well as better timing traffic lights for those remaining on Route 29.

As the Southeast looks to accommodate the projected growth in the region in coming years, there will be ample opportunity for planners and decision-makers to consider expanding highways or, more wisely, avoiding the pitfalls of induced demand and embracing the many alternative solutions available.  

SELC’s Land and Community Program tackles the growth challenges and decisions shaping the Southeast. This series of posts runs every other week and highlights the broader issues driving this work—transportation and land use developments, alternatives, and progress in our region. Click the links below to read previous posts.