Traffic Stop (© Corbis)Click to enlarge picture

For 50 years, drivers have been dreading the sight of flashing red lights in their rearview mirrors. With modern technology, that anxiety is only going to deepen. Until you get to court, that is.

For the half-century since radar guns first started picking off lead-footed drivers on America's highways, the speed trap has been an unseemly topic. To the busted, it's what it sounds like — a dirty kind of ambush, often employing a sudden drop in the legal speed limit to set the trap, and a traffic officer's sniperlike trigger pull to seal the deal. To municipalities and law enforcement agencies, it's not a trap but a necessary evil, and a crucial deterrent to keep rampant, potentially dangerous speeders in constant fear for their licenses. The fact that it rakes in cash for the city, county or state just makes it a win-win for the good guys. Today, the ongoing duel between radar-and-laser-detecting drivers and cash-strapped municipalities is about to become even more one-sided, as states are approving the use of automated, unattended speed cameras. But what most drivers don't realize is that they never really stood a chance to begin with.

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Radar Days Gone By
In most parts of the United States, the classic speed trap — the cop parked behind cover, firing off bursts of radar waves or lasers as targets whip into view — is a cultural relic, an outmoded myth of speed enforcement. The static radar-gun setup has largely been replaced by car-mounted "rolling radar" systems, aimed across the highway median at multiple lanes of oncoming traffic. These devices measure the closing speed of a given target, and subtract the speed of the officer's own car. If the resulting number is high enough, the officer will cross the median and hit the siren. There's no warning, no slammed brakes as a stopped squad car appears from behind an embankment. "The online speed-trap registries and GPS coordinates of known traps — enthusiasts like them," says Craig Peterson, a police instructor and consultant who tests police radar systems as well as radar detectors. "But you might as well be back in the old days, on a CB radio. It's anecdotal evidence. 'I saw an officer at Dairy Queen; watch your back.' Sorry, that's not going to help you." In reality, the moment of truth is a cross between a joust and a shootout, and an exchange you're usually aware of only if you're operating a radar detector.

Bing: View Pictures: Fixed Speed Traps

Another enforcement technique that most drivers will never see coming is the trusty old stopwatch. A number of police agencies around the country continue to use aerial units to spot speeders, the plane and chopper pilots easily picking out the fastest offenders, and tracking the time it takes them to cross a given set of lines in the road. As with rolling radar, the first and only sign of trouble will be flashing lights in the mirror, leading you to wonder which roadside trap you missed.

Laser Guns at Rush Hour
That's not to say the speed trap is extinct. Static traps are still the norm in population-dense areas such as the Northeast, where long, straight stretches of roadway are rare and where Jersey barriers and other highway dividers can prevent officers from looping around to pursue a speeding vehicle. Still, even these old-school holdouts are evolving — while radar remains the dominant technology for static enforcement, laser-based systems are becoming cheaper every year, and increasingly popular. Why? Instead of firing a wide beam across two or three lanes of traffic, a lidar (light detection and ranging) gun hits an individual target with an infrared laser beam one meter wide or thinner, even pinpointing a vehicle as it weaves through heavy traffic.

Bing: Learn About Lidar Speed Detection Devices

Last year, Colorado-based Laser Technology Inc., one of the country's leading lidar gun makers, released the TruCam, which captures video as it tracks targets. The result is ironclad legal evidence, showing exactly which vehicle was in the gun's sights, and how fast it was traveling. Radar systems, by comparison, are more subjective, sometimes requiring a human to determine which target among a wide swath of vehicles is actually moving the fastest. And lidar has another major advantage, Peterson says — the newest systems are so precise that they can track the distance between two cars, allowing officers to issue violations for tailgating, a major cause of serious accidents.

Have you ever been caught in a speed trap?

Tomorrow's Unattended Traps
If rolling radar, laser guns and the occasional flying stopwatch are replacing the old-school static radar trap, a new trend in traffic enforcement is poised to redefine the way speeding tickets are issued. Speed cameras, devices that automatically detect an offending vehicle with lidar or radar and snap a photo of its license plate, are in use in select counties in more than a dozen states. These aren't limited pilot programs: In Lafayette, La., speed cameras issued 114,748 speed violations in less than a year and a half. And last year, Arizona approved the use of speed cameras across the entire state.

Click to enlarge pictureChevrolet Caprice Police Car (© General Motors)

In most parts of the United States, the classic speed trap — the cop parked behind cover, firing off bursts of radar waves or lasers as targets whip into view — is a cultural relic, replaced by car-mounted "rolling radar" systems, aimed across the highway median at multiple lanes of oncoming traffic.

From both a technical and a legal standpoint, speed cameras are the inheritors of a longstanding tradition of automated enforcement. Thousands of red-light cameras have popped up around the country in recent years, along with a growing fleet of semi-automated roving photo vans. These unmarked vehicles aren't driven or operated by police — they're parked along the side of the road and act like vehicle-mounted speed cameras, using a combination of still cameras, video, lidar and/or radar to detect and document offending vehicles.

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Tomorrow's automated systems promise to be even stealthier, with companies unveiling designs that range from discreet, streetlight-mounted devices to a camera and strobe light hidden inside an orange traffic barrel. "This storm didn't really get started until three years ago, when states started having budget problems," Peterson says. "I guarantee you, this trend is not going to be reversed any time soon. Under the guise of public safety, you can make a staggering amount of money."

An Aggressive Defense
As the business of speed violations moves further away from flesh-and-blood law enforcement and into the outsourced world of automated cameras, the rules of engagement have changed. For drivers who feel preyed on by overzealous policies or faulty cameras, there are two options. First, you can avoid the fight in the first place, capitalizing on the fixed nature of most speed cameras. Web sites such as speedtrap.org, where users provide tips about suspected speed traps they've come across, become far more useful as a log of permanently installed systems throughout the country.

Bing: Learn About Speed Trap Laws

For a more high-tech approach, combination radar-laser detectors, which are legal everywhere but Virginia (unlike jammers, which are banned widely), have a chance of picking up radar and lasers from today's automated systems, but only if the gadget is sufficiently sensitive, and correspondingly pricey. But possibly the most useful anti-speed cam feature of a product such as Escort's $500 Passport 9500 ix (one of the best performers at Peterson's site, radartest.com), is the ability to sound an alarm based on the GPS locations of known fixed cameras, since by the time their narrow, short-range beams are detected, it's often too late.

Drivers can also fight automated enforcement by doing what the machines can't: show up in court. "We recommend to our members to plead not guilty, presuming you have the time and resources to stand up for your rights," says Gary Biller, executive director of the National Motorists Association, an advocacy group that lobbies for less restrictive traffic laws. "We find that if you put on a pretty healthy defense, like asking when the last time a camera was serviced and for proof it was calibrated correctly, we see that a lot of times the court system doesn't like traffic violations to take a lot of time." If your main goal is to keep points off your license, point out that a license-plate image doesn't prove who was behind the wheel.

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The NMA estimates that about 90 percent of drivers simply pay their fine, take the insurance hit and move on. By becoming part of that vocal 10 percent, and with no human officer to contend with in court, the odds of striking some kind of deal go up exponentially. This isn't always as cynical as it sounds. Biller says that many of the NMA's members believe they were ticketed in error. And there are problems that have nothing to do with the calibration of a given camera. In Arizona, the licenses of thousands of drivers were suspended because of automatically generated tickets that never showed up in the mail (authorities must now serve all such tickets in person).

Have you ever been caught in a speed trap?

The future of the speed trap is really the death of human speed enforcement and the population boom of speed cameras, whether parked tactically or installed strategically. For now, fighting back means knowing where they are, and deciding whether it's worth questioning their accuracy in court. That's now. But in the decades to come, as the speed camera becomes as ubiquitous as convenience-store security cameras, those online registries won't be warning which roads are being watched, but hailing the few roads that aren't.

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Based out of the Boston area, Erik Sofge is frequent contributor to Popular Mechanics and Slate.com. He specializes in everything scientific and technical.

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