Here’s a video to prove it.

At locations where rubber bumpers have been installed, preliminary data show injuries and deaths have dropped “significantly faster” than at other intersections, says Rob Viola, director of safety policy and research at the city’s department of transportation (DOT).

This redesign is simple, but it took years of research to figure out. Now other US cities, including San Francisco and Los Angeles, are copying New York’s innovation.

The danger of left turns

“Left turns are one of the most dangerous things that drivers do all the time,” says Matthew Roe, director of the Designing Cities Initiative at the National Association of City Transportation Officials.

New York combed through more than 1,000 traffic-crash reports to understand and quantify the dangers surrounding left turns. It found that left-turning vehicles caused three times as many pedestrian and biker casualties as right-turning vehicles. Left turns were cited in 13% of the city’s pedestrian and biker deaths from 2010 to 2014. Among street-safety design professionals, the danger of this maneuver has been known for years, but New York was among the first to pin down why.

The city’s DOT found that left turns are dangerous for three reasons. First, a car’s frame blinds its driver during a left turn, much more than during a right. Second, drivers drive faster when making left turns because they have a wider radius than with right turns. Third, drivers cut corners during their turns.

The poor visibility makes crashes more likely. The speed makes crashes more fatal. And cutting corners expands the area of crosswalk where pedestrians can get hit—once again making a crash more likely.

In response to these findings, the DOT launched the Left Turn Traffic Calming program and created different intersection redesigns to target each of these issues:

The Basic Hardened Centerline, which includes the rubber bump, slows down drivers and discourages them from cutting corners.

The Slow Turn Wedge uses markings and flexible plastic posts to buffer pedestrians from traffic and shrink the area where they could get hit by a car.

The Complete Hardened Centerline (jokingly dubbed “the Deluxe treatment”) combines the basic hardened centerline and slow turn wedge.

Since the program’s launch in 2016, the DOT has updated 217 intersections, targeting those with the highest left-turn crash rates. An early analysis of the before and after crash data has already returned promising results. But Viola says the DOT will continue to review crash reports to verify that the reductions are in fact due to fewer left-turn crashes.

The cost to implement these intersection redesigns ranges from a couple hundred to a few thousand dollars, drastically less than the tens or hundreds of thousands spent on typical street-redesign projects, which can involve new curbs, pavement, and signals.

“This is something that cities can do without waiting for the money to dig up an entire street, figure out how drainage works and how to change an intersection entirely,” says Roe. “We’ve been impressed with the scale of transformation.”

A systems-based approach

New York not only innovated these redesigns, it also took a new approach to studying and addressing traffic safety.

“Traditionally, in the world of traffic safety, you would take a more reactive approach: Where have the problems been in the past? Let’s focus on those areas or issues,” explains Leah Shahum, founder and director of the Vision Zero Network, a US nonprofit focused on helping cities eliminate pedestrian deaths.

New York, in contrast, looked for system-wide trends in the data, then figured out solutions to directly address those trends. This allowed the city to quickly identify and discern the differences between problem intersections and deploy its solutions at a large scale.

Since New York’s demonstration of this approach, other cities have quickly followed in its footsteps, Shahum says. Some have even replicated the left-turn program. Los Angeles is now testing the hardened centerline and slow turn wedge in its downtown areas, according to its transportation department. Officials in San Francisco say they also recently kicked off a data-driven effort to develop left-turn calming devices specific to the city’s needs.

Vision Zero

The left-turn program is part of New York’s Vision Zero initiative. Vision Zero began as a traffic safety concept in Sweden in the late 1990s to challenge the acceptance of injuries and deaths as an inevitable byproduct of the convenience of motorized travel. (The Vision Zero Network is named after the initiative.)

In 2014, New York became the first US city to adopt the effort after advocacy groups successfully turned it into a campaign issue during the mayoral election. When the new mayor, Bill de Blasio, entered office, he committed to eliminating traffic deaths within a decade.

“It drew all the parts of the city together, all the different agencies, even state agencies,” says Viola. The previous administration, under Michael Bloomberg, laid the groundwork for data-driven safety planning and policymaking. Those efforts expanded under the new initiative. “It was really effective in that it became this more universal project endorsed by the mayor. That’s allowed us to coordinate things that weren’t possible before and be more ambitious,” Viola says.

Since Vision Zero’s introduction, the city has made several large-scale changes to eliminate deaths, including reducing the speed limit to 25 miles per hour (40 km/h), changing the timing of traffic lights to give pedestrians a head start over turning cars, and performing around 100 street-redesign projects per year. As a result, New York’s traffic death count has fallen every year to a cumulative total of 34.6% since 2014.

Not everyone is satisfied with the progress. Critics worry the administration isn’t working fast enough to reach its 10-year goal. Jack Davies, for example, a staffer at New York-based nonprofit Transportation Alternatives, is impatient to see the left-turn program scale. “There are about 13,000 intersections in the city that are busy enough that they’ve warranted a traffic light. It’s been two years since the pilot was initially rolled out, and we’re still at just 217 intersections,” he says. “The data conclusively shows that these interventions save lives, so why aren’t we rolling them out?”

Viola admits that more work could be done. “There are always new challenges for us to take on.”

But for the vast majority of the US Vision-Zero community, New York is lauded as a success story that has inspired other cities to follow in its footsteps. Over the past few years, Roe has noticed an important shift in the traffic-safety community. “One of the ideas that has spread like wildfire around the country is that when you empower your city DOT to make changes, when you say your job is to make the streets safe, they’ll do it and they’ll do it well.

“New York was one of the early cities to demonstrate that that was possible.”