Online calculator reveals increased congestion from highway expansions

State Departments of Transportation are anxiously awaiting a federal infrastructure bill to move forward with projects. According to some transportation groups, highways expansions should not be among them.

On Wednesday, Oct. 20, the Rocky Mountain Institute, in partnership with the Natural Resources Defense Council and Transportation for America, released a State Highway Induced Frequency of Travel (SHIFT) Calculator. The calculator allows anyone to see the potential increase in traffic and pollution resulting from highway expansions.

According to the institute, highway expansions not only do nothing to relieve congestion, but in fact do the complete opposite.

“Over the past few decades, taxpayer dollars have funded billions of dollars in highway expansions intended to alleviate road congestion, but it usually does not take long for the traffic to return,” the Rocky Mountain Institute states in a news release. “This endless loop, known as ‘induced demand,’ fails to address congestion while leading to more cars on the road and more pollution from the transportation sector, which is the nation’s largest source of emissions.”

The theory of induced demand is oftentimes cited by proponents of tolls.

In theory, highway expansions decrease congestion by allowing vehicles to travel in more lanes. Consequently, vehicles are spread out more thinly.

However, that only works if the same number of vehicles travel on more lanes. Induced demand argues that the availability of more lanes with less congestion attracts more motorists. Eventually, the increase in motorists nullifies the benefits of more lanes.

The transportation groups encourage transportation agencies to use the calculator to account for induced demand when planning and implementing highway projects.

For example, adding 15 interstate lane-miles in Midland, Texas, will add 40-60 million additional vehicle miles traveled each year. That is equal to emissions from 5,100 additional passenger cars and light trucks. A similar expansion on other freeways and expressways in Midland County may add 17-26 million vehicles miles traveled each year.

“For 90 years, we have known that building new lanes creates new vehicle trips that fill those lanes, and for 90 years, we have mostly ignored this fundamental law while repeating the same mistakes at great cost,” Beth Osborne, director of Transportation for America, said in a statement. “We must stop making empty promises about congestion reduction that never materialize. Having the ability to estimate added travel caused by expansions can finally equip decision makers and the public with the data to make the case for something more effective at connecting people to jobs and opportunity.”

Calculations estimate long-term changes (5-10 years) from induced vehicle miles traveled and emissions as a result of a highway expansion. Numbers are based on existing lane mileage and vehicle miles traveled data from the Federal Highway Administration. LL