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Should San Bruno Widen Skyline Boulevard?

Highway 35 as seen on Google Street View

Highway 35 as seen on Google Street View

San Bruno commuters who drive on Highway 35 (Skyline Boulevard) may be familiar with congestion if they use that road at rush hour. Traffic backs up there at peak commute times, particularly in the southbound direction on weekday mornings and the northbound direction in the evening. In an attempt to alleviate the congestion, the San Mateo County Transportation Authority is proposing widening the highway to four lanes between Sneath Lane and I-280. According to the preliminary planning study, it is expected to cost at least $35 million to widen the 1.4-mile stretch.

At first glance, this sounds like a no-brainer: let’s just add some capacity to the road, we’ll eliminate the bottleneck, and then the traffic will flow faster. Problem solved. But when you look at the research on highway expansions, it becomes clear that this approach is probably not the best one.

For decades, we have been widening highways in the United States in an effort to reduce congestion, but economists and transportation planners have learned that this technique is almost never effective in the long run. There is a well-studied phenomenon called “induced demand” or “induced travel.” When you widen a road, that initially reduces travel times, but the faster travel attracts more motorists. Within just a few years, there are enough additional vehicles on the road to increase congestion back up to level it was before the expansion ever happened. On top of that, taxpayers have taken on the long-term financial liability of maintaining miles of additional pavement.

A 2015 research summary on the Caltrans website said the following about increasing highway capacity: “Numerous studies have examined the effectiveness of this approach and consistently show that adding capacity to roadways fails to alleviate congestion for long because it actually increases vehicle miles traveled (VMT).” That same report noted that highway expansions substantially increase greenhouse gas emissions, despite an initial reduction that may result from vehicles spending less time idling.

Our neighbors in Pacifica recently had to grapple with a similar decision. Caltrans and the Transportation Authority proposed widening Highway 1 between Fassler Avenue and Reina del Mar, making it six lanes instead of just four. A grassroots organization, Pacificans for Highway 1 Alternatives (PH1A), ultimately prevailed in getting the widening shelved, in favor of studying more modern techniques for alleviating the congestion.

“Pacifica rejected Caltrans’ plan to widen Highway 1 because people realized that it ultimately would not save time or reduce congestion,” said former Pacifica mayor and PH1A member Peter Loeb. “The time lost during multi-year construction would not be made up, and induced demand would quickly result in congestion being back to the same level as before widening.” Pacifica has instead started implementing Intelligent Traffic Systems, a way of using technology to optimize traffic flow without widening any roadways. “Along with most traffic engineers, Caltrans has begun to recognize that highway widening and expansion is an outmoded approach to congestion management that does not solve the problem,” said Loeb.

With respect to the proposed Highway 35 widening, the San Bruno City Council is expected to vote soon on whether to proceed to the next phase of the project.

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