How fast drivers go on San Mateo's surveyed streets

This spring the city measured traffic on 123 segments of its larger streets. On 55 of them, the fastest 15% of drivers went at least 5 mph over the limit. On 16, they went fast enough that the survey proposes raising the limit for everyone.

How a speed survey sets the limit

On larger streets, California ties the speed limit to the speed the fastest 15% of drivers exceed, called the 85th-percentile speed. The limit is that speed rounded to the nearest 5 mph, minus reductions the law allows (Vehicle Code 22358.6). Drivers going slower than that speed don't change it. When the fastest 15% speed up, the next survey can raise the limit again. A survey is valid for 7 years (Vehicle Code 40802).

Since 2022, state law (AB 43) has let cities round down, keep a current limit, or cut 5 mph more on streets with crash histories or many people walking and biking. Each street's page lists the options that apply and what each requires.

For a person walking, the average risk of death is about 10% if struck at 23 mph and about 25% if struck at 32 mph. These are impact speeds, the speed at the moment of the crash (AAA Foundation for Traffic Safety, Tefft 2011).

The map

Each line is a surveyed segment, colored by how far the fastest 15% go over the posted limit. On 60 of the 123, half of drivers go faster than the limit. Tap a line to open that street.

• At or under the limit
• 1 to 4 mph over
• 5 to 7 mph over
• More than 7 mph over

All 123 surveyed segments

Speeds in mph. "Half go faster than" is the median speed; "Fastest 15% go faster than" is the 85th percentile. Tap a column heading to sort.

"Lowest legal option" may depend on a city finding or a records check; each street's page says what's needed. Where the survey sheet and the city's summary disagree, the street's page notes it.

Is your street missing?

Most San Mateo streets weren't surveyed. On most residential streets, state law sets a 25 mph limit without a survey (Vehicle Code 22352), so the city surveys only larger streets where it posts other limits. All 123 segments here are arterials or collectors. If your street isn't listed, it wasn't measured in this survey.