Last month, Caltrans linked to a policy brief that sought to address whether more highways means less traffic congestion. Needless to say, the brief didn’t go viral, but it’s piquing curiosity as word gets out. Most state Departments of Transportation endorse the idea that building more roads spurs “economic benefits” and relieves traffic, but California, as it often does, bucks that trend.
[jump] Written by UC Davis professor Susan Handy, the brief’s thesis is pretty simple: more roads mean more traffic — a phenomenon called “induced travel”:
The basic economic principles of supply and demand explain this phenomenon: adding capacity decreases travel time, in effect lowering the ‘price’ of driving; and when prices go down, the quantity of driving goes up. Induced travel counteracts the effectiveness of capacity expansion as a strategy for alleviating traffic congestion and offsets in part or in whole reductions in GHG emissions that would result from reduced congestion.
So, to summarize, building more roads means more traffic and more greenhouse gas emissions. This isn’t what many states want you to believe.
As CityLab notes, just last month Connecticut’s Department of Transportation announced it was widening two interstates, a project that would collectively save travelers 18.7 million hours of delays by the year 2040.
Connecticut is probably wrong.
State DOTs are also fond of touting the economic boons that new highways bring. But, again, there’s no compelling evidence to support those claims. Per the brief:
Most studies of the impact of capacity expansion on development in a metropolitan region find no net increase in employment or other economic activity, though investments do influence where within a
region development occurs.
In fact, reducing road capacity tends to bring economic benefits without worsening traffic. The brief specifically calls out an example from San Francisco: “the removal of elevated freeway segments coupled with improvements to the at-grade Embarcadero and Octavia Boulevards,” which revitalized the area while also relieving traffic.
According to the brief, much of the traffic on new roads is itself new. Some drivers ditch their old, slower routes for the new ones, while others are apparently cruising for the hell of it. After all, the “price” of driving is lower when the state hacks out new highways.
“A capacity expansion of 10% is likely to increase VMT [vehicle miles traveled] by 3% to 6% in the short-run and 6% to 10% in the long-run,” the brief states. Short-run changes will manifest within five years, while long-run effects can take up to 10 years.
The impact of “induced travel” has “yet to filter into [Caltrans’] thinking and decision making,” according to CityLab, quoting from a 2014 assessment from the State Smart Transportation Initiative. But with lots of roadwork planned or in-progress, now's the time for Caltrans to take the long view.