The Great Plains, with all that flat, wide-open and sparsely populated land, has long had the most generous — or audacious — speed limits in the country. Cross the Minnesota border into South Dakota, and the default statewide speed limit on the interstates there, as of this spring, is now 80 miles an hour.

Idaho, Wyoming and Utah have also pushed their legal limits that far. Texas, meanwhile, has a toll road that tops out at 85. Which, as we all know, means there are drivers there traveling 90. The Missouri River, as it turns out, is a kind of speed-limit fault line: Most states west of it consider legal what Virginia, Ohio and Illinois would call "speeding."

The above map, from MetricMaps, illustrates that abrupt division using local speed limit data collected by Navteq (which powers a lot of in-car navigation tools) and provided by the mapping platform Caliper. That map shows the maximum local speed limit for any local roads or highways in each Census block group in the U.S. (that's a unit of geography smaller than many neighborhoods). If a highway passes by your house, in other words, your neighborhood may look dark blue.

The nationwide contrasts are striking, but so are the local ones: Zoom in to an individual city like Los Angeles, and the darker arteries effectively outline highways.

Zoom into Washington, D.C., and low-speed local roads dominate. Even massive highways that run through the city, like Interstate 395, are relatively slow at 40 miles per hour. Outside the city, the outline of the Beltway emerges:


New York City, which lowered its default speed limit to 25 miles per hour last year (after this data was collected), is also mostly composed of slower local roads :


Contrast that picture with Houston, where even the slowest parts of town aren't that slow, relative to New York or D.C.:


These maps, through the lens of speed limits, reflect the hierarchy of how we build roads, from local residential streets, to busier boulevards, to limited-access arterials and high-speed highways. Each environment demands different standards. But this national map also raises a question central to "vision zero" campaigns trying to end pedestrian deaths and make roads safer: Does it make sense that a residential neighborhood in Houston would allow faster traffic than a residential neighborhood in Brooklyn?

Sure, there are cultural differences between one part of the country and another, as well as contrasts in topography and development patterns. But the cost of collisions — what happens when someone is hit at 25 miles per hour vs. 30 or 40 — holds constant across the country.