Engineering judgment… factors not apparent… curves… driveways… transition… because we want to. Reading speed limit studies for California cities reminded me of the excuses engineers use when they don’t want to do their job.
Based on an unscientific survey, about two-thirds of California municipal traffic engineers and consultants aren’t doing their job. Or they consider their job to be telling politicians what they want to hear.
In California speed limits on major city streets have to be based on facts, not politics. This is supposed to be the case elsewhere, but California is special because of the speed trap law. If the speed limit doesn’t meet state standards, you beat the ticket even if you were driving dangerously fast. (This does not apply on freeways posted 65 or 70, 25 mph school zones, or low volume side streets, but it does apply to major city streets.)
Specifically, the city has to have a recent engineering study justifying the speed limit. And it has to follow the standards in the California Manual On Uniform Traffic Control Devices.
The speed limit should be as close as possible to the 85th percentile speed of free-flowing traffic. In practice this means about 5 mph above the average speed. Cities are now allowed to round down instead of up without making excuses (this is a recent compromise forced by the state legislature).
Speed limits 5-7 mph below the 85th percentile speed require documentation of special circumstances. These circumstances are supposed to be factors not readily apparent to drivers that are not reflected in normal operating speed. (CVC 22358.5) Drivers can see roadside development, but they can’t see a high accident rate.
Reductions more than 7 mph are not allowed. If the 85th percentile speed is 43, the speed limit can’t be 35.
Reading Santa Monica’s latest review I noticed the phrase “factors readily apparent” appeared in both places where percentile speeds were mentioned. That’s shorthand for the legislatively authorized reason to go more than 4 mph below the 85th percentile speed. Seeing it used in every case suggests engineers are treating it as the administrator password to bypass rules, and it isn’t that.
When I looked at Mountain View’s speed limit reviews a few years ago they were the same: always the maximum reduction no matter whether it was justified under the circumstances.
There are worse cases. The city of Ripon recently approved a bogus pseudo-engineering review. I count 11 violations of state standards, 7 of them illegal reductions no matter what the excuse and 4 of them insufficient excuses.
Did they not know about state standards, or did they not care?
To quote federal standards, “Uniformity of the meaning of traffic control devices is vital to their effectiveness.” To quote me, “an agency gains credibility by usually doing the right thing.” To quote Aesop, if you cry “wolf!” too many times people will stop believing you.
Speed trap law aside, these cities do not have credible speed limits.
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