Market Street Has More Bike Traffic Than You Thought

The Market Street bicycle counter has been undercounting two-wheeled traffic -- and not because of a computer glitch. Starting last month, the counter reported a huge jump in bike commuters. How come? All indications point to a recent tweak to the bike lane that guides more riders over the counter's underground sensor.

On several days this year, the counter has tallied nearly 4,500 people cycling eastbound on Market at Ninth Street. On most weekdays, at least 3,700 riders have been counted. That's about 1,000 more riders, on average, than were counted each day last January.

Last month may have been California's driest January on record, but weather doesn't explain the jump. Even in the warmest months last year, ridership typically ranged from 2,700 to 3,200. Prior to 2015, the record was 4,045, set on August 7 last year.

So what changed in the first week of January? The SFMTA installed plastic posts along the bike lane's edge that guide bike riders to stay in the bike lane and roll over the bike sensor. Previously, many bike commuters passing by the counter rode outside the bike lane, instead using the adjacent traffic lane since it was closed to cars in 2009.

SFMTA spokesperson Ben Jose said that based on the agency's manual bike counts, the bike counter remains about 95 percent accurate, the same rate as before. It's "plausible" the posts explain the recent jump in the bike count, he said. No other likely explanation has been put forth, though the SFMTA has yet to verify with the counter's manufacturer that it does not need to be recalibrated.

Getting a better read on Market Street bike traffic is one more way the SFMTA is improving the understanding of how San Franciscans' travel habits are changing. Earlier this month, the agency reported its new survey methodology has revealed that most trips in the city are made without a private automobile.

Hat tip to Joe Chojnacki for pointing out the data jump.