In a true fairy tale of a transportation project, Texas spent a measly $4.25 million widening a highway and, in defiance of conventional wisdom among transportation planners, doubled the speed of rush hour traffic on a notoriously congested highway in Dallas.

The Texas Department of Transportation repaved the shoulders along both sides of a 6.3-mile stretch of State Highway 161 between Dallas and Fort Worth in September. Then it opened them up to traffic during the daily rush hour, keeping tow trucks on standby in case someone breaks down. Based on figures released this month, with the extra lanes in place, traffic “started sailing,” *The Dallas Morning News *reported this week.

It isn't supposed to work that way. The rule of induced demand says widening highways does not ease congestion, and often makes it worse. Transportation officials could see this anomaly as a Texas-sized reason to build more highways—but shouldn't.

This "is an awfully unique situation," says Todd Litman, executive director of the Victoria Transport Policy Institute in Victoria, British Columbia. The project wasn't a traditional highway widening, nor was it a permanent fix—though the agency is looking for funding for a more permanent widening project. And Texas hasn't seen the full effect of its work.

The Science of Traffic

More lanes often means more traffic because people like to go places, as long as the threat of bumper to bumper doesn't dissuade them. Widening a highway may ease the pressure, but only until everyone learns of the quick, new route about town.

Civil engineers liken traffic to a gas: It expands to fill the space provided. As civil engineer and sustainability advocate Charles Marohn so eloquently put it, “Trying to solve congestion by making roadways wider is like trying to solve obesity by buying bigger pants."

Such thinking is common among urban planners, and even DOT officials in car-crazy California admit they can't build their way out of congestion. Of course, not everyone's onboard. "It took a really long time for the medical community to give up on bloodletting," says Litman. "Name your outdated medical treatment or scientific theory and you can find people who stuck with the old paradigm. This is one of those situations where [expanding freeways] really is a paradigm."

Dallas Bucks the Trend?

Two things might explain why the Dallas project worked. The first is that the bottleneck on that highway was a very specific problem: a two-lane stretch connecting three-lane highways. Opening the shoulders eliminated the choke points of squeezing into a tighter space.

The second and more cynical explanation for the project's success is that it wasn't actually successful. The traffic numbers published this month include just a few days after the new lanes opened in September. Traffic has increased since then, though the TxDOT says traffic is still moving faster than before the project. It’s quite possible unbearable congestion will return, as more locals change their behavior to take advantage of what is suddenly a smooth ride—that's the fundamental principle of induced demand.

Luckily, demand management doesn't necessarily mean pouring billions into a light rail system (though new light rail systems are nice). There are easier solutions. Congestion charges limit traffic in crowded areas. Dynamic tolling can encourage people to drive outside rush hours. (Both drum up extra cash for dwindling city coffers.) Lanes reserved for buses or carpools can disincentivize driving alone and improve traffic flow.

These traffic-taming ideas have been around for decades. But they feel kooky-crazy, because so few American transportation officials are using them. Highways are necessary, and cities are right to search for tweaks that make them more pleasant and effective. But at some point, that means providing alternatives. Because "more!" doesn't work.