Are Speed Cameras Effective?

To justify saturating the state with speed cameras, minions from the State of Arizona have endlessly echoed the mantra of the speed-camera lobby: 1) Most accidents are speed-related, 2) Speed cameras slow traffic and 3) Slower traffic means fewer accidents.

Never mind that even Roger Vanderpool, the state's top cop, has written that speeding is a negligible problem, even while his Department of Public Safety makes high-profile arrests for alleged speed camera violations. Even the feds' distorted numbers from the National Highway Traffic Safety Administration (NHTSA) and its Fatality Analysis Reporting System (FARS) show that speed in excess of the posted limit is accountable for a tiny percentage of accidents.

But for the sake of argument let's momentarily suspend disbelief and say they're at least partially right, a sentiment not universally shared. Accurate statistics of accidents at camera locations won't be available for some time yet, but now that scores of speed cameras and a fleet of 100 photo radar vans have been deployed, it certainly isn't difficult to measure the cameras' effect on freeway speeds.

Over a period of weeks this spring I conducted traffic surveys near speed vans and fixed cameras in several locations around the metropolitan Phoenix area. I did the same in Mesa, Glendale, Prescott Valley and Star Valley, Arizona. To create before/after speeds, I first measured speeds one half mile before the camera, then at the same distance after the camera. If the speed camera tub-thumpers are right, the after speeds should be noticeably slower.

I conducted the surveys using accepted Institute of Transportation Engineers (ITE) methodologies, measuring speeds with a Kustom Signals Pro Laser III speed laser linked to a laptop with LaserStat traffic-survey software. (Using $5,000 worth of sophisticated equipment isn't required; the ITE deems acceptable the use of a $200 radar gun and manually recording speeds on a clipboard, the most common method employed.)

Unlike radar, which usually clocks the strongest target, the $3,500 laser can single out any vehicle within range. This allowed the targeting of only free-flowing traffic, eliminating slow-moving trucks and increasing the accuracy of the survey. I sampled cars equally from each travel lane and to make the statistics even more unimpeachable, I recorded the speeds of at least 200 vehicles at each location, twice the number dictated by ITE guidelines. Once back in the office the LaserStat program generated spreadsheets and graphs from the data, everything from 50th percentile speeds to 10 MPH Pace speeds.

Interestingly, the numbers from every site were nearly identical. In this composite chart of representative results from four of the freeway locations, it can be seen that far from slowing traffic, the cameras had no effect on freeway speeds. In fact, at some locations average speeds were higher after the cameras. Okay, the small increases are statistically insignificant. But the numbers are clear: speed cameras do not decrease highway speeds. Aside from a brief dab at the brakes by a few drivers in reaction to fixed speed cameras—frequently resulting in screeching tires from cars behind—most seemed oblivious to them. Hardly any slowed in reaction to the speed vans.

The survey numbers also illustrate the fallacy of the state's claim that cameras are needed to battle widespread speeding on Arizona freeways. Average speeds on the 65-zoned Loops were remarkably law-abiding. Loop 101 was an even 65 mph; on Loop 202 it was 67.5 mph. (That's as high as it gets. On weekdays between 6:30 a.m. and 10:00 a.m. and between 3:30 p.m. and 7:00 p.m. average speeds are substantially lower, a fact known to anyone who's driven on traffic-choked Phoenix freeways.)

Significantly, the 85th percentile speed on most sections of Loop 101 was 70 mph; on Loop 202 it was 71 mph. On Scottsdale's portion of Loop 101 where the SEP "trial project" cameras were located, it was 73.4 mph. (The cameras flashed at 76 mph.)

The 85th percentile speed is that at which 85 percent of all drivers are traveling.. A cornerstone of ITE guidelines for nearly half a century has been that speed limits should be set as close as possible to the 85th percentile. My traffic surveys show that if the limit were correctly set at 70 mph, there would be hardly any violations for the cameras to record. (Had the speed limit on Scottsdale's section of Loop 101 been correctly set at 75 mph, it likewise would have witnessed virtually no violations.)

This begs the questions: If speeding isn't a problem and speed cameras have zero influence on speeds, what are the cameras for?

Related story: The Majority Favors Speed Cameras?

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