Shoppers walk in downtown Seattle. Jason Redmond/Reuters

It would be the latest city to slow down drivers in the name of Vision Zero. But how effective will it be?

Seattle is slowing down: Speed limits will drop from 30 to 25 mph along main corridors and from 25 to 20 mph on residential roads, assuming officials approve a recent move by a city council member. If all goes according to plan, crews could start erecting signs as soon as November, says the Seattle Times.

That would make Seattle the latest in a list of cities to trim vehicle speeds in the name of “Vision Zero,” the urban policy platform calling for an end to all traffic fatalities, which have risen dramatically in the U.S. in the past few years. At least seventeen cities around the U.S. have officially adopted the stance, which involves engineering roads for safer mobility, ramping up traffic enforcement (for better or worse), and educating drivers, cyclists, and pedestrians alike. Boston moved earlier this week to lower its default street speed from 30 to 25 mph. New York City enacted the same limits in 2014, and San Francisco is attempting to do the same.

There are questions about how effective these slowdowns are. Research has shown cutting speeds can lead to fewer accidents and fatalities. A pedestrian struck by a car traveling 30 mph has a 45 percent chance of being seriously injured or killed—a probability that drops to just 5 percent at 20 mph, one widely-cited UK study found. But it’s not clear that the 25 mph default that Seattle and other U.S. cities have chosen for their busiest streets will make a huge difference, given that motorist behavior may not be dramatically affected. In fact, one test by officials in Minneapolis found that reducing limits from 30 mph to 25 mph along a bike route produced only negligible changes in traffic speeds.

Lowering posted speed limits isn’t the only thing the Emerald City is doing to crash-proof its streets, though. Traffic-calming measures such as road humps and road diets, as well as targeted law enforcement around school safety zones, are also supposed to help it reach its ambitious goal of eliminating all traffic fatalities by 2030.

Currently, the numbers are going in the wrong direction, as traffic deaths actually went up in 2015. The new speed limits might help get things get back on track—and also rake in some much-needed cash. New York City reaped a record $1.9 billion in fees and fines last year, largely thanks to ramped-up traffic enforcement. City officials would likely protest such ulterior motives, especially given that traffic fines disproportionately impact the poor (who also tend to be most affected by unsafe streets). But Vision Zero, in addition to saving lives, can also be quite the revenue stream.

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