The most obvious benefit to slower speed limits in cities is improved safety. Fewer crashes and injuries including collisions with bicycles can be expected.
But there are other several other possible gains that can be realized by forcing drivers to slow down on congested city streets, according to a recent CityLab article. Ironically, one might be to enable people to get around faster.
If separated but narrower travel lanes with 15 mph speed limits that prioritize non-cars are created, more people might opt for electric scooters and bicycles, which can outpace cars in the most congested streets. (The average car in midtown Manhattan creeps along at just 4.7 mph.)
Slower speeds would also make it safer and more practical to deploy autonomous vehicles. Several U.S. cities have reduced speed limits and New York has revived its program to enforce speed limits by cameras in school zones.