Police radar operates by transmitting radio waves at a fixed frequency. A portion of the beam reflects from a target vehicle and returns to the radar. If the target is moving, a slight change in frequency occurs (Doppler shift). The radar does the heavy math and calculates target speed.
The picture gets more complicated if both radar vehicle and target are moving, the task for which moving radar was created in the early seventies by some very clever boffins at industry heavyweight Kustom Signals.
How Radar is Used
Two types of radar are used—stationary and moving. Stationary radar must be used from a static site, typically a patrol car parked alongside the road. The most common sort of stationary-only radar is the hand-held model popularized by decades of photographs of officers holding them, often pointed toward the camera, like giant pistols.
Newer radar models have two features that make them particularly lethal. Same Lane mode allows the officer to clock same-direction vehicles ahead of the rolling cruiser. If the radar has a rear antenna it can clock faster vehicles as they come up from behind.
Fastest Speed mode allows the radar to sample multiple targets and display the speed of the fastest. Using this feature it's easy to clock a motorcycle passing an eighteen-wheeler, an impossible feat for conventional radar. Learn more about this type of radar.
With a single exception, moving radar is the tool of choice for state highway patrols. In Pennsylvania, the law permits only the State Police to use radar and then only in stationary mode. Hand-held radar, usually K-band Decatur models, have been the mainstay of the Pennsylvania State Police for years.
Without access to radar, many local police and sheriff's departments in the state use time/distance computers like VASCAR. These time a vehicle between two reference points and display its average speed. The technology works fine, but it's a lot more labor-intensive than just pointing a radar gun toward the target.
Newer radar models have two features that make them particularly lethal. Same Lane mode allows the officer to clock same-direction vehicles ahead of the rolling cruiser.
Fastest Speed mode allows the radar to sample multiple targets and display the speed of the fastest. Forget about hiding behind slower cars. Learn more about this type of radar.
Radar can transmit continuously or be placed on hold, ready to fire but not transmitting. With no signal present there's nothing to detect, neutralizing a radar detector. When a target draws near, a button-press on the remote triggers the radar and a speed appears almost instantly.
Officer preference dictates the choice. Some let it run constantly, content to get fewer customers except for the brain-dead. Aggressive officers are more likely to use instant-on, hoping to outwit drivers with detectors.
North American radar can operate on X, K or Ka band. About one percent of the 100,000-odd radar in service nationwide use X band, 15 percent use K band and the rest operate on Ka band.
How Far Away Can it Get Me?
On a busy highway, in moving mode the typical clock occurs at less than 1,000 feet, usually much closer. Radar is dumb, merely displaying a speed, and it's the officer's responsibility to determine which vehicle is producing that speed. Legally at least, he's required to establish a tracking history, a multi-step process to verify that he and the radar are looking at the same target.
Done properly, this can take several seconds, more than enough time for an alert, radar detector-equipped driver to spike the brakes. Learn more about radar range.
Places To Expect Radar
On highways without a divider the most common encounter is to meet a cruiser approaching from the opposite direction. If traffic volume is moderate-to-heavy, it's common for the officer to drive in the fast lane to prevent other vehicles from blocking the radar beam.
If you're driving on a highway with a center divider, look for radar in a cruiser parked on your side of the highway. A center divider prevents the U-turn necessary for officers to work opposite-lane traffic in moving mode. Instead they'll sit at roadside.
A high-quality radar detector can usually spot radar from miles away. These are expensive—$350 to $650—but one can pay for itself in a day. A cheap detector—anything priced below $300—might work acceptably well when conditions are perfect. But expect to be pestered with false alarms and don't be shocked when it doesn't utter a peep sometimes before you see flashing lights in the mirror.
- Long range
- Advanced K-band filtering
- Nuisance signal lockout
- Red light camera alerts
- Online updates, no obsolescence
Features to Look For
If you commute or drive often near a city, pick a model with GPS. The satellite technology lets you lock out nuisance signals like automatic door openers. Without GPS it'll alert every time you pass within half a mile of a Walmart. View the best GPS-enabled detectors.
Something else to look for: Good K-band filtering. Without it, expect to be plagued by endless false alarms. A lot of these can be blamed on Blind Spot Monitoring (BSM) systems on cars. Most use radar, warning the driver when a lane change is risky.
Some police radar guns use the same K-band frequency, but their number is tiny compared to perhaps 10 million BSM radar and another 500,000 door openers in service. The problem continues to worsen as BSM radar appears on an increasing number of cars.
For example, of the K-band alerts we logged during one 1,300-mile road trip recently, 99 percent were caused by BSM radar. Four alerts were from roadside radar message trailers. None was a police radar gun.