Better Traffic Flow Is a Two-Way Street

Cities such as Dallas, Denver, Sacramento and Tampa are reversing course on their one-way streets for a number of reasons; but improving traffic flow likely isn't one of them. Eric Jaffe looks at a recent study that upends conventional wisdom.

While two-way streets may be more attractive for their livability, ease of navigation, safety, and economics, the conventional wisdom is that one-way streets are better for traffic flow. However in a recent paper published in the Transportation Research Record, Vikash Gayah, a civil engineer at Penn State University, makes the case that two-way streets can also improve congestion.

"The typical metric of traffic is vehicle flow — which amounts, more or less, to standing on the corner and counting how many cars go by," explains Jaffe. "Flow is high on one-way streets because there's little reason for cars to slow down. But flow doesn't take into account the fact that traveling through one-way street systems often means taking a circuitous route, which adds distance to every trip."

"You can move more vehicles through a roadway, but if they have to travel a longer distance, in the end, you have actually fewer people being able to get to their destination and get off the road," says Gayah.

"So [based on Gayah's theories] cities looking to improve trip capacity in downtown areas have some options," suggests Jaffe. "Smaller cities, with shorter average trip lengths, should be able to reduce congestion by converting one-way streets into two-way streets (with a couple options for left turns). Larger cities, with longer trip distances, should consider a shift to two-way systems that ban left turns entirely."

Thanks to Erica Gutierrez

Full Story: The Case Against One-Way Streets

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