The most obvious immediate benefit to a fundamentally slower city is the safety boost it delivers. Reducing speeds is the best, easiest, and fastest way to quickly radically improve safety, for both drivers and anyone in front of them.
To get one, simply dropping speed limits isn’t the answer; street design itself—not enforcement or signage—is the most powerful governor of driver behavior. When Streetsblog compared studies looking at neighborhood slow zones in New York and London, the Big Apple didn’t see a significant drop in injuries, but London enjoyed benefits because they implemented serious traffic-calming infrastructure changes, such as raised crosswalks and street-narrowing curb extensions.
A lot of bike and pedestrian advocates will also argue that Americans are just doing speed limits wrong. Most state DOTs typically follow a rough measure known as the 85th percentile rule. Traffic engineers conduct studies measuring the average speed of drivers on a road, then they set speed limits so that 85 percent of those drivers would be traveling under the speed limit. That idea, as FiveThirtyEight detailed in 2015, effectively sets a minimum speed rather than a maximum. In 2017, the National Transportation Safety Board recommended that the Federal Highway Administration scrap the guideline in favor of other road factors like crash history or pedestrian counts.
