Still, it's nearly impossible to know whether the rate of crashes is changing. Since there isn't precise data on how many people are riding and how frequently, a jump in the absolute number of crashes doesn't necessarily say much about overall bike safety.
Moreover, crashes are typically reported only if someone is transported to a hospital, or if a car needs to be towed.
"It's going to be very hard to have hard empirical data that's going to prove" the law is working, says Miller, a cyclist and the bill's prime sponsor. Still, he adds, "From my own observation, I have noticed people being much more careful while overtaking a bicyclist, so I do believe the law is having an impact."
Undercover in Austin
One police officer in Austin, Texas, is leading the charge on enforcing safe-passing laws. Armed with a pole that measures compliance with Austin's 3-foot passing law, officer Rheannon Cunningham devised an undercover sting operation, which resulted in a nearly 12-fold increase in citations — and calls from departments around the country interested in replicating her efforts.
"The cyclists always felt like the police never did anything to enforce the laws [that] were there to protect them," Cunningham explains. And if drivers "don't feel like they're going to get caught or stopped for something, they will push the envelope. They'll blow it off."
Cunningham's operation works like this: Two plainclothes police officers on unmarked bikes ride along a half-mile stretch of road that has no bike lane, but is close to popular bike routes.
Whenever a car passes within three feet — something the officers are trained to judge using the pole — they would radio a marked patrol car ahead that would pull over the offending driver. (The undercover officers recorded the encounters on bike-mounted cameras in case of challenge.)
"I didn't get the feeling that people did it on purpose," says Cunningham, who participated as an undercover officer in the operation. "There's just very poor judgment on how close they passed you."
Ironically, Cunningham says, it was the cyclists caught behind the wheel who were most indignant. "Their argument was: 'We're cyclists, we know how close we passed you,' when in fact they didn't."
Fewer than 10 people were cited in Austin between 2009 and May 2013, when the sting operation started. At least 117 people have been pulled over since, Cunningham says, and 78 of them were let off with warnings to "reinforce our message of education over purely punitive enforcement." Cited drivers were allowed to take a "defensive cycling" class to get the $175 ticket dismissed.
"It's really hard to know that the operation directly affected the outcome, but I know our collisions dropped and fatalities did not increase," Cunningham notes.
For his part, Pittsburgh's Cmdr. Holmes says the Austin model "is something to be considered." He is working on refreshing his officers on bike laws in advance of the construction of a protected bike lane Downtown on Penn Avenue.
It is unclear what the wider police bureau's position is on enforcement of bike laws. Holmes said he could not speak for the department outside his zone, and Pittsburgh police spokesperson Sonya Toler declined comment after being contacted multiple times.
Eventually, though, the law may not be enforced by humans at all, predicts Anthony Rowe, an electrical and computer engineering professor at Carnegie Mellon University.
"The assumption going in is that they're going to be mandating transponders in cars" that communicate with everything from traffic lights to other cars, says Rowe, who is part of CMU's "Safe Cyclist" project. "If cars are going to have these types of radios on them [...] they could actually communicate to and from bicycles as well."
Alerts could be built in that notify drivers if they are venturing into the 4-foot zone — in effect creating virtual bike lanes, Rowe says. And using software loaded onto a smartphones, bikers could be alerted to close-passing cars as well. Such technology, if widely adopted, "could be transformational for safety," Rowe says.
In the long run, enforcing safe-passing laws will likely become a matter of programming, Rowe says: "Once cars become autonomous" — capable of driving themselves under computer guidance — "there's no reason why they won't automatically avoid cyclists."
But in the short term, Rowe explains, the technology could generate data that shows where cars are most likely to pass within the 4-foot zone, giving police a leg up on targeted enforcement. And in the immediate future, League of American Bicyclists legal specialist Ken McLeod stresses that safe-passing laws signify a willingness among governments to grab low-hanging legislative fruit, making room for larger initiatives down the road.
"Making it clear that bicycles need and deserve space on the roadway [is] a recent phenomenon" McLeod says. "We're just starting that journey."