Study: Johns Hopkins Says Shrinking Streets Could Improve Safety

Matt Posky
by Matt Posky

A Johns Hopkins School of Public Health’s Bloomberg American Health Initiative study, published late last year, has suggested that narrow streets are safer than wider ones.

It sounds counterintuitive. But let us dig in to see how the report came together.

Researchers examined 7,670 sections of pavement in Dallas, New York City, Philadelphia, Salt Lake City, Miami, Denver, and Washington D.C. that offered comparable levels of daily traffic. The stretches of pavement were likewise said to have “21 key roadway design characteristics” to be examined. This included items like on-street parking and the number of lanes. Then, researchers randomly selected 1,117 of those streets for the study.

Data was referenced against Google satellite imagery and the crash data provided by local officials, with researchers analyzing “the relationship between lane width and the number of crashes that occurred in each road section from 2017 to 2019.” Special attention was said to be given to roadway characteristics that might be relevant.

The resulting analysis was then used to create policy recommendations for urban planners. This included things like reducing the number of lanes, narrowing pre-existing lanes, and lower speed limits on stretches of road that do not serve as a major transit or freight corridor. It also recommended setting the standard lane width at 10 feet in low-speed urban settings, asking cit leaders to provide justification for wider lanes.

The Hopkins-Bloomberg joint also prompted city and state transportation departments to establish a context-appropriate speed before determining lane width while city planners “prioritize inclusive street design rather than driving speed and functionality.” Ideally, the paper suggests repurposing driving lanes into bike paths or wider sidewalks.

From the study:

Local and state departments of transportation have long favored lane widths between 11 and 12 feet for city streets with the assumption that the extra space is safer and can accommodate pedestrians and cyclists. In an analysis of 1,117 streets in the seven cities, the authors found that reducing city traffic lane width to 9 feet, especially in traffic lanes with speed limits up to 35 miles per hour, could help reduce traffic-related collisions. Reducing lane width would also create more space for other safety and livability features, such as bicycle lanes and wider sidewalks.
The authors found that the number of vehicle crashes do not significantly change in streets with a lane width of 9 feet compared to streets with lane widths of 10 feet or 11 feet. There are significant increases in crashes — approximately 1.5 times higher — when the lane width increases from 9 feet to 12 feet.
The researchers also found no significant changes in car crashes with wider traffic lanes in a speed limit zone of 20–25 miles per hour. However, traffic lanes with 10-, 11-, and 12-foot lane widths have significantly higher crashes than lanes that are 9 feet wide in zones that are 30–35 miles per hour.

Unfortunately, the data is accompanied by the typical Vision Zero agenda that prioritizes minimizing the space allotted for cars in a bid to reduce emissions and create more space for pedestrians, cyclists, and public transportation. While some of the aspects of the plan are indeed wise, especially those that focus on minimizing interactions between motor vehicles and everyone else, the end result typically ends in recommendations that make driving less convenient — things like encouraging congestion charging, removing lanes, adding car-free urban zones, and installing more automated modes of traffic enforcement.

“Our study of city lane widths found that contrary to the current thinking, wider lanes in urban areas can lead to a higher number of crashes and ultimately fatalities,” said Shima Hamidi, PhD, Bloomberg Assistant Professor of American Health and director of the Center for Climate-Smart Transportation at the Bloomberg School. “What if we can narrow lanes without sacrificing safety, and how can we best use the additional space in the existing infrastructure? That’s what we want to know.”

We’d like to know that too. But there is a sense that the team may have been conducting research to legitimize a desired action, rather than simply being on the prowl for useful data. This is also the kind of thing the Bipartisan Infrastructure Law/Infrastructure Investment and Jobs Act (passed by the Biden administration in 2021) seems to have been created for. In addition to boosting the NHTSA budget by 50 percent, it also created $5 billion in appropriated funds under the Streets and Roads for All (SS4A) grant program.

The Vision Zero Network has praised the SS4A scheme endlessly, noting it quite literally paves the way for fundamentally changing the manner in which we conceive American roadways. It wants to do away with our traditional enforcement, education, engineering, and reliance on emergency services (calling them the four Es of the past). Instead, Vision Zero believes modern roadway safety can reach a point where vehicular fatalities are totally eliminated by shifting toward safe speeds (lower speed limits), safe streets (automated, camera-based enforcement), safe vehicles (automated vehicles with on-board cameras and electronic safety nets), and safe people (the kind that limit their interactions with automobiles).

“Lane-width reduction is the easiest and most cost-effective way to accommodate better sidewalk and bike lanes within the existing roadway infrastructure,” said Hamidi. “Narrower lanes ultimately minimize construction and road maintenance and also reduce environmental impacts.”

These types of studies are always tough because the above plan will very obviously make urban motoring less feasible. But your author has done enough city driving to know that some places could benefit from making more space. Certain aspects of the plan do indeed seem wise. But it's not obvious that they'd be of any real utility outside of the most densely populated urban areas and the regulators seem fairly keen to see things deployed on a national level.

The smattering of sound concepts are likewise undermined with this technocratic bend that would have policing and the cars themselves become automated. Sadly, adding more technology into vehicles hasn’t coincided with reduced on-road fatalities. If you track the data, U.S. crash rates actually seem to increase rather dramatically around the same time touch screens became ubiquitous in automobiles and smartphone proliferation peaked. Meanwhile, autonomous vehicles have not matured as promised by the industry.

[Image: Stephan Guarch/]

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Matt Posky
Matt Posky

A staunch consumer advocate tracking industry trends and regulation. Before joining TTAC, Matt spent a decade working for marketing and research firms based in NYC. Clients included several of the world’s largest automakers, global tire brands, and aftermarket part suppliers. Dissatisfied with the corporate world and resentful of having to wear suits everyday, he pivoted to writing about cars. Since then, that man has become an ardent supporter of the right-to-repair movement, been interviewed on the auto industry by national radio broadcasts, driven more rental cars than anyone ever should, participated in amateur rallying events, and received the requisite minimum training as sanctioned by the SCCA. Handy with a wrench, Matt grew up surrounded by Detroit auto workers and managed to get a pizza delivery job before he was legally eligible. He later found himself driving box trucks through Manhattan, guaranteeing future sympathy for actual truckers. He continues to conduct research pertaining to the automotive sector as an independent contractor and has since moved back to his native Michigan, closer to where the cars are born. A contrarian, Matt claims to prefer understeer — stating that front and all-wheel drive vehicles cater best to his driving style.

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  • VoGhost Fantastic work by Honda design. When I first saw the pictures, I thought "Is that a second gen Acura NSX?"
  • V16 2025 VW GLI...or 2025 Honda Civic SI? Same target audience, similar price points. Both are rays of sun in the gray world of SUV'S.
  • FreedMike Said this before and I'll say it again: I'm not that exercised about this whole "pay for a subscription" thing, as long as the deal's reasonable. And here's how you make it reasonable: offer it a monthly charge. Let's say that adaptive headlights are a $500 option on this vehicle, and the subscription is $15 a month, or $540 over a three year lease. So you try the feature for a month, and if you like it, you keep it; if you don't, then you discontinue it, like a Netflix subscription. In any case, you didn't get charged $500 up front the feature. That's not a bad deal.In my case, let's say VW offers an over the air chip reflash that gives me another 25 hp. The total price of the upgrade is $1,000 (which is what a reflash would cost you in the aftermarket). If they offered me a one time monthly subscription for $50 to try it out, I'd take it. In other words, maybe the news isn't all bad.
  • 2ACL A good car, but - at least in this configuration -not one that should command a premium. Its qualities just aren't as enduring as those of Honda's contemporary sports cars. For better or worse, this is a formula they remain able to replicate.
  • Jalop1991 I just read that Tesla's profits are WAY down "as the electric vehicle company has faced both more EV competition from established automakers and a slowing of overall EV sales growth." This Cadillac wouldn't help Tesla at all, but the slowing market of EV sales overall means this should be a halo/boutique car. Regardless, yes, they should make it.