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February 13, 2011 / Jim Fenton

‘Radar Enforced’: False Advertising

Speed Limit 25 Radar Enforced

Typical Speed Sign

California, car haven that it is, has long placed restrictions on the use of use of radar for enforcement of speed restrictions.  One of these restrictions is a prohibition on the use of radar in what are defined as speed traps (California Vehicle Code sections 40800-40808). With exceptions that include local streets and school zones, if the speed limit is not justified by an engineering and traffic survey, it is presumed that the speed limit might have been set artificially low, creating a speed trap, and evidence from radar and similar electronic measurement means is not admissible in speeding cases. In most cases, this justification requires that the 85th percentile speed (the speed that 85% of the cars drive at or slower than) can be no more than 5 miles per hour over the speed limit.

This came to my attention recently when I was reading a draft of the Los Altos Collector Traffic Calming Plan [19 MB PDF]. An Existing Conditions map on page 5 of that plan shows the current posted speeds and 85th percentile speeds for the collector streets (smaller than arterials, but larger than neighborhood streets).  None of the streets shown had 85th percentile speeds that were within 5 mph of the posted speeds.  The 85th percentile speeds ranged from 7 to as much as 14 mph over the posted speed.  Presumably this means that radar evidence cannot be used in traffic court.  Nevertheless, speed signs like that shown are common, proclaiming radar enforcement where it can’t be used.

I’m not saying this to advertise that it’s safe to speed in Los Altos. Please don’t; we want everyone to be safe and the traffic calming measures that are being proposed are onerous enough as it is.  Of course, the reason for putting up Radar Enforced signs is to provide extra encouragement to drivers to slow down. Obviously this isn’t working in Los Altos, as evidenced by these measured speeds.  If radar enforcement cannot legally be done, posting Radar Enforced signs is just diluting their effectiveness.  These signs are so common that people just don’t see them any more; they might as well not be there.

Speed Limit 25 Violators Tortured

Is this sign less true?

Suppose there was this (Photoshopped) speed limit sign instead.  Obviously, they’re not going to put this sign up; they’re not going to torture anyone.  But on the other hand they’re not going to use radar either.  Is it more harmful to put an obvious false statement on a sign or a falsehood that is more plausible?  The latter may be cause the greater harm, if one discounts the possibility that drivers swerve upon seeing the “Violators Tortured” sign.

I would like to see a requirement that Radar Enforced signs only appear where it is actually legal to use radar.  Drivers will start to notice them if they aren’t as numerous and actually mean something.  Cities would also have an additional incentive to set reasonable speed limits for the driving conditions.

[Updated 3/15/13 with correct link and title to Collector Traffic Calming Plan]

[updated 8/13/15 with re-corrected link and correct PDF size]

[updated 10/16/20 with correct link to California Vehicle Code]


Leave a Comment
  1. Ellen Finch / Feb 16 2011 10:59 am

    I like your alternative. I’ve been meaning to get back to the areas of Sunnyvale suburbia that have interesting speed limit signs along the lines of which you speak (but more publicly acceptable, and funny). If I can find them again. I’d be interested to know whether they work better than the usual speed limit signs.

  2. AL CATRAZ / Feb 27 2018 7:18 am

    I thought that POLICE HAVE TO NOTIFY US when the place a RADAR TRAP!
    By putting signs everywhere they NEGATE the warning… since the SIGNS stay and the RADAR goes, you still don’t know WHEN they do use a RADAR & when NOT!

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