How this was made

The survey

Source. City of San Mateo Engineering and Traffic Survey summary sheets, prepared by DKS Associates and signed by a registered engineer in August 2026, obtained through a public records request: the full PDF (20 MB). One sheet per segment, 123 segments.
Dates. Speeds were measured March 10, 2026 to July 17, 2026. Each street's page gives its survey date.
What the sheets report. Posted and recommended limits, the 50th- and 85th-percentile speeds, the 10 mph pace, average daily traffic, and 2021–2025 collisions. They do not report how many vehicles were measured, so no sample sizes are shown.
How it was read. Most pages are scans, so the numbers were read by optical character recognition and then checked. On every sheet, the printed collision rate is reproduced from the collision count, daily traffic and segment length. The 85th-percentile speed and recommended limit match the sheet's written recommendation wherever it was legible, and the rest were checked by eye. A short list of hand corrections is in the code.
Where the city's documents differ. On four segments, the survey sheet and the city's summary for the September 22, 2026 council meeting (Attachment 3) disagree about the current or proposed limit. These pages use the survey sheet and note the difference on each.

Each segment's options apply California Vehicle Code sections 22358.6 (rounding and documented reductions), 22358.7 (an extra 5 mph on safety corridors or near places that draw people walking and biking) and 22358.8 (keeping the current limit), with the California Manual on Uniform Traffic Control Devices (2026), section 2B.21.
"No further finding" means the survey's own 85th-percentile speed already allows that limit. The other options depend on facts the survey doesn't record, and each lists what is needed. Business district limits (section 22358.9) were not assessed. Limits below 20 mph are not shown.
The reasoning, the statute text and every source are in the legal memo. This is a reading of the statutes, not legal advice.

Typical effects come from the Federal Highway Administration's Proven Safety Countermeasures fact sheets (2021) and the Traffic Calming ePrimer, Module 4. Copies are in the repository.
Street types are the survey's own classification (minor arterial or major collector). The city's traffic calming policy goes by the General Plan's classification, which was not checked segment by segment.
The pedestrian risk figures are from Tefft, B.C. (2011), Impact Speed and a Pedestrian's Risk of Severe Injury or Death, AAA Foundation for Traffic Safety.

Segments are drawn on OpenStreetMap streets between the survey's cross streets, choosing the path whose length best matches the sheet. 6 segments end at a ramp, walkway, trail or the city limit and are placed partly by length. Map data © OpenStreetMap contributors (ODbL); tiles by OpenFreeMap.
"Ask the city" emails go to the council members whose districts the segment crosses (district boundaries from the city) and to the staff contact named on the speed limit update. Council members as of October 25, 2026.