Six weeks after he announced his plan to promote safe cycling in New York City, Mayor Bill de Blasio told reporters on Wednesday afternoon that he was mulling the idea of forcing Citi Bike riders to wear helmets, and having all cyclists obtain licenses — measures that have been shown to discourage cycling rates in other major cities.

CBS 2's Marcia Kramer — who once told her viewers, "Imagine if the man on the bike was a terrorist!" — asked de Blasio about the idea of requiring helmets for Citi Bike riders, "given the fact there have been a lot of bicycle deaths."

"I have thought about that. And that’s something we are talking about inside the administration," de Blasio replied. "There are different viewpoints on what would work and how much impact it would have. But I think it’s a real valid issue so it’s something we are studying right now."

But Kramer pressed on: "Is it something that you think you should require? I mean, it just seems to me you drive down the street and people for whatever reason don’t always obey the bike lanes, don’t always obey lights or the right way of going down the streets, imperiling themselves."

"I think it’s like everything else in this place, we have to think about what is going to be safe for people first, but also what’s going to work. And I think the big questions are is it something we could actually enforce effectively, would it encourage or discourage people from riding bikes?" the mayor said. "But I care first and foremost about safety so we are having that discussion right now. I think it is a really valid issue. We have got to figure it out."

Since Citi Bike launched in 2013, the system has seen 85 million rides and just two fatalities, one of which was found to have been caused by a bus driver who swerved into the cyclist, Dan Hanegby, in Midtown in 2017. Victor Ang died of his injuries after being struck by a truck driver in Midtown earlier this year. In 2019 alone, 21 cyclists have been killed on New York City streets, eleven more than in all of 2018.

"We're proud of Citi Bike's remarkable safety record over the past six years and encourage our riders to wear helmets," said Julie Wood, a spokesperson for Lyft and Citi Bike. "There is extensive evidence that what keeps cyclists safe are protected bike lanes, enforcement against dangerous driver behavior, and more people riding bikes—not mandatory helmet laws."

Helmet laws have been cited in the demise of Seattle and Melbourne, Australia's bike share initiatives.

Correction: This post has been updated to reflect that there have been 21 cyclists killed on NYC streets in 2019 so far.

Moral: If you want bike riders to live, build safer streets. If you want bike share to die, require helmets. — Janette Sadik-Khan (@JSadikKhan) January 17, 2017

A study published in 2015 found that New York City cyclists wearing helmets were less likely to require a head CT scan at the hospital after a crash, and of those that did receive a CT scan, helmeted bicyclists had lower rates of serious head injuries. But evidence also strongly suggests that helmet laws depress cycling rates, which in turn negatively affects the "safety in numbers" phenomenon crucial to safe cycling.

In 2003, Peter Jacobsen, writing in BMJ, defined "safety in numbers" for cyclists this way:

The likelihood that a given person walking or bicycling will be struck by a motorist varies inversely with the amount of walking or bicycling. This pattern is consistent across communities of varying size, from specific intersections to cities and countries, and across time periods.

In 2009, researcher Piet De Jong found that helmet laws in safe cycling cities have a negative health impact, while in unsafe cycling cities, they do not make it significantly safer for cyclists to ride. (You can read more on mandatory helmet laws here and here.)

Later on in the press conference, another reporter asked the mayor if he had considered requiring cyclists to obtain licenses, an idea that has been kicked around the City Council before. "I have not, but I think it's also a valid discussion," de Blasio said.

"I'm someone who believes that more and more people riding bikes has been a good thing for the city in terms of reducing the number of cars on the road, taking pressure off other forms of mass transit, it's better for the environment, it's good for people's health, a lot of people want to do it," the mayor added. "But we have to make sense of the safety realities and that's what Vision Zero is all about. First and foremost it's about enforcement on the motor vehicles, where we have the central problem. We are gonna keep expanding enforcement on bicycles as well, because we have a lot of bike riders who have to remember they have to follow the rules."

Setting aside the regulatory infrastructure necessary to make licensing cyclists a reality, the enforcement component seems destined to fall on the communities who normally bear the brunt of cycling enforcement: immigrants and minorities.

"The Mayor sadly appears to not only be abandoning his signature life-saving Vision Zero policies, but with comments like this appears to be actively working against Vision Zero, street safety and Citi Bike—one of the most successful and popular public transit modes in our city," said Marco Conner, the co-deputy director for Transportation Alternatives.

"With his overture to requiring bike licenses he is, once again, showing a willingness to recreate stop-and-frisk through other means in New York City, given the NYPD's proven racially disparate bicyclist ticketing history in predominantly Black and Brown neighborhoods."

"However, if the mayor is seeking to create a safer environment where pedestrians and bicyclists can move safely throughout New York, he should prioritize the rapid implementation of his Green Wave plan, and further prioritize action on Vision Zero to ensure that no more New Yorkers fall victim to car violence," Connor continued. "To date, more than 80 pedestrians and bicyclists have been killed on the streets of New York, a significant increase from 2018.”