Lowering the Speed Limit
Q: Can you lower the speed limit on this road?
A: The City is generally unable to lower the speed limit of streets without performing an engineering study. The setting of speed limits is carefully regulated by the California Vehicle Code (CVC) and the California Manual on Uniform Traffic Control Devices (CA MUTCD). The CA MUTCD provides uniform standards and specifications for all official traffic control devices (e.g., signs and pavement markings) in the State of California, including speed limit signs.
Under CVC Section 22352, some types of streets can be assigned speed limits of 25 or 15 miles per hour (mph), based on their roadway classification or location relative to specific land uses (e.g., alleys, residential or business districts, next to schools). Other streets must have speed limits set by local statute based on an Engineering and Traffic Survey (E&TS), also known as a speed study. Where no speed limit is set and prima facie speeds of 15 or 25 mph do not apply under CVC Section 22352, the basic speed law (CVC Section 22350) applies: “No person shall drive a vehicle upon a highway at a speed greater than is reasonable or prudent having due regard for weather, visibility, the traffic on, and the surface and width of, the highway, and in no event at a speed which endangers the safety of persons or property.”
The City is required by law to periodically perform E&TSs to set and maintain enforceability of speed limits, as required by the CVC and CA MUTCD. Current statutory speed limits are specified in the City’s Code of Ordinances, Chapter 11.68, found here. In order for statutory speed limits to be enforceable, they must be set based on an E&TS performed using radar spot speeds and conducted within the last few years, and the speed limit must be posted on each end of the roadway segment.
An E&TS utilizes radar spot speeds, roadway and area characteristics, daily traffic volumes, and collision histories to recommend speed limits on each study roadway segment. Speeds are set based on the 85th percentile speed, as outlined in CA MUTCD Section 2B.13. There are strict limits for when a speed limit may be set below the 85th percentile speed, rounded to the nearest 5 mph. The 85th percentile speed, or critical speed, is typically considered the safe operating speed of a roadway based on roadway characteristics readily apparent to drivers. Speeds set below the 85th percentile must be carefully selected, typically based on factors not readily apparent to drivers. As noted in the CA MUTCD, studies have shown that setting the speed limit below the 85th percentile speed generally increases collision rates.