In 2019 Mountain View adopted a Vision Zero policy.

This policy does not have many specific actionable items. I am proposing one here: lower the speed limit on residential streets from 25mph to 20mph.

25mph sign

  • It is safer
  • It reduces pedestrian and cyclist stress
  • It reduces noise levels

The main point is safety. Vision Zero is about reducing fatalities (to zero).

Portland, as part of its own Vision Zero, reduced speed limits to 20mph on most of its streets back in 2018

Seattle did similar in 2016

Minneapolis and St Paul did in 2020

So did DC

Nearly all of them have a graph like this:


A study of the reduction to 20mph (30kmh) speed limits in Bristol starting in 2010 found

strong evidence of a city-wide reduction of fatal injuries of around 63%

And ProPublica has an interactive graph based on AAA data.

Additionally, NACTO recommends 20mph on any street designated as a “bike boulevard”. Currently no street in Mountain View meets this recommendation.

Slower speeds reduce the number of “passing events”, which are both stressful and dangerous (many fatal injuries happen when a vehicle is overtaking a cyclist)


  • Residential streets should be for local traffic. 20mph is fast enough.
  • Many studies have found 20mph to be safer, and many cities have already implemented 20mph speed limits
  • 20mph speed limits would encourage walking and cycling, and reduce noise and pollution from cars


Just changing the speed limit signs alone will not be enough, traffic calming will be necessary in many streets, since they are designed for and encourage faster speeds.

I will write more on traffic calming in the future.