Let me start with an admission: yesterday, while riding a bike, I slowed down a car.
Riding through the Presidio, I descended Lincoln Boulevard from the Golden Gate Bridge to Baker Beach at 25 m.p.h. This stretch of Lincoln has no downhill bike lane, just “Bikes May Use Full Lane” signs and sharrows reminding bicyclists to ride in the center of the lane. Lincoln has a 30 m.p.h. speed limit, meaning the driver behind me, who like nearly all road users was courteous and didn’t honk or complain, could have traversed this 1-mile stretch 30 seconds faster if I didn’t exist. (30 seconds might sound like nothing, but Bay Area governments routinely spend tens of millions of dollars rebuilding roads because of delays on this scale.)
Bike advocates often feel the need to spend time, energy, and ink proving that bikes and bike infrastructure usually don’t slow down cars. The Active Transportation Alliance featured the claim that bike lanes slow traffic as a top biking myth to debunk in a recent article. Traffic studies in Manhattan and Chicago, widely publicized by People for Bikes and other advocacy organizations, have found that protected bike lanes have either had no effect on traffic speeds or led to slightly faster traffic even when general traffic lanes were removed to build the bike lanes. Research consistently shows that the primary causes of slow car traffic are too many cars and poor street design and that adding car lanes alone doesn’t solve the problem.