The eight lane Highway 101 partitions the San Francisco Peninsula with an eight lane wall of traffic from San Jose to San Francisco. The Caltrain line with its 50,000 daily commuters runs to the west of 101. Businesses, jobs and residential areas can be on either side of the highway. Many of the three percent of Bay Area commuters who ride bikes must find a way to cross this highway.

Consider Hillsdale Boulevard in San Mateo, California, which is fairly typical of many 101 crossings. In this from Google Maps aerial view, Hillsdale crosses from the lower left to the upper right of this image.

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