There is a public-health crisis unfolding before our eyes in the United States, where the simple act of walking has become a life-threatening proposition. Recently, a pedestrian killed by an automated vehicle in Arizona made national headlines, but that was just the tip of the iceberg: The same week, 10 other people were killed while walking -- just in Arizona. Across the country, the number of people who died while walking increased by nearly 50 percent from 2009 to 2016, from just over 4,000 to almost 6,000, at a time when traffic fatalities declined in many of our peer countries, including Britain and Canada.

What can be done? It turns out that the culprit is quite clear.

According to a recent report from the Insurance Institute for Highway Safety, almost the entire increase in pedestrian fatalities in the U.S. occurred on the 4 percent of streets in cities and suburbs that are wide and designed to carry heavy traffic, technically known as arterials. These are places designed for cars to run at expressway speeds, yet they are also where an increasing number of people live, work, go to school and shop. In many places, these high-speed roads are the local "main street."

Arterials don't have to be death traps. These main roadways can be redesigned for both safety and efficient movement of traffic, and some cities are showing the way. In 2013, a group of the nation's top city street designers from around the country assembled the Urban Street Design Guide, a blueprint for designing safe, livable city streets that has since been endorsed by the Federal Highway Administration. The design tools that work are about making roadways the right size, whether by eliminating or narrowing traffic lanes or adding curb bulb-outs to give people walking a shorter distance to cross.

These changes and their impact are not just hypothetical. In New York City, 186 people were killed on Queens Boulevard between 1990 and 2014. But a targeted investment in redesigning that road has had dramatic safety impacts. The project removed excess travel lanes, added more and better crosswalks, marked protected bike lanes, created refuge islands for people crossing the street, and redesigned transitions between the main road and the service road. In the three and a half years since the city completed the final improvements, there has not been a single traffic fatality on what was once called "the Boulevard of Death."

Rainier Avenue in Seattle has a similar story. Between 2004 and 2014, 11 people were killed in traffic crashes on a four-mile section, triggering a call in 2015 for a new look at those deaths and the conditions that caused them. The result of the study was a reinvention of the street. Engineers made it easier and safer for people to walk across the street by eliminating one moving lane, installing left-turn bays and signals at intersections, improving bus facilities and reducing the speed limit from 30 mph to 25. Since the project was implemented, there has not been a single fatality on that stretch of Rainier Avenue. Meanwhile, speeding has decreased dramatically and travel is more reliable: Buses are traveling the corridor as much as a minute faster than they were before the redesign.

The dramatic increase in traffic deaths on arterials since 2009 should be a clarion call to action: The way we design heavily traveled streets in the United States needs to change. Cities have some success stories, and we should have more. It's time that states and the federal government work together with our cities and focus on the unsustainable, unsafe way that we design our large urban and suburban streets before thousands more die.