2/24/2010

02-24-10 - Police Laser and Countermeasures

I did a bunch of research into police laser (lidar) and countermeasures, so I thought I'd share.

Police laser is infrared and is a pretty wide beam. At 1000-2000 feet (typical shooting distance) the beam will be a few feet wide. Unlike radar guns, they have to be stationary to use and can't shoot through glass, so the cop actually has to get out of the car and stand there and aim at you specifically. The laser has to bounce off something on your car and get back to the gun to be picked up.

Modern detectors like the V1 can detect laser, though on its own this is basically useless because when it alerts you have already been shot. Unlike radar, there is no detectable scatter. The V1 also false-alarms from sudden changes in illumination such as a reflection of the sun shining on it.

Cops are taught to aim at the license plate, but it's a myth that the plate is the only thing that can be picked up, it's just a good reflector and also a good center target (sort of like aiming your gun at the chest). Most cops and old guns only shoot cars from the front, but new guns and new technique will shoot the rears of cars. Many semi-intelligent people think that laser guns require a straight facing surface to get a reflection back, so they use tricks like angling their plate downward toward the ground. This does not work, because many surfaces on cars are retro-reflective ; that is, they have a BRDF with a large lobe directly backward towards the direction of incident light. License plates typically have retroreflective paint on them, and car headlights and tail lights are parabaloid mirrors which makes them great retroreflectors.

What can you do to avoid laser tickets?

1. Speed in the rain. Since cops actually have to get out and stand and shoot you, they don't do it in the rain. They would rather sit in the car and use the radar gun.

2. Stealth your car. This is theoretically possible to do, but very hard, and most of the commercial countermeasures are snake oil (things like the "Veil" diffusing paint coating or "Laser Shield" prizmatic license plate cover (Veil is basically sticky plastic goo that gives surfaces micro dimples so they scatter light randomly, Laser Shield is ridged plastic plate cover so it reflects light out to the sides)). To really successfully stealth your car you would have to do something like this :

Buy a car that's as small and curvy as possible (eg. an SUV is hopeless), you want lots of angled surfaces like a stealth fighter. Paint your car matte black (no gloss clear coat that will retroreflect). Replace your headlights with bright LEDs or something that doesn't use mirror reflectors. Replace all the glass with very flow reflectance or diffusing plexiglass. Remove your license plate, photo copy it and print it out on hard plastic or something so you eliminate the retroreflective paint.

While this is possible, it's pretty ridiculous and the halfway measures do almost nothing. Also some of those steps are of course illegal, but the thinking in the laser avoidance community is that it's better to get a non-moving-violation ticket for an illegal license plate or lights instead of a moving violation for speeding.

3. Install jammers. These do seem to be real. Radar jammers are illegal everywhere in the US, but laser jammers are legal in most states. Basically they work by having an IR emitter in the same band installed all over the car which makes the gun show an error code. The recommended technique is to use them with an on/off switch and a detector like the V1, so when you get a laser detection, you slow down then turn off your jammer so that the cop can then read you at legal speed.

Laser jammers do not work if they are mounted concealed, they must be mounted with the heads prominent, preferrably 4-6 heads at key points on the front and rear. The best jammer appears to be "Laser Interceptor" , and that runs about $2000 installed.

Cost/benefit says the jammer is not worth it unless you already have several tickets and are at risk of going into the hazardous driver insurance pool or losing your license. (or live in a state like Oregon where it's hard to use a lawyer to get out of tickets).

BTW as an aside it annoys me that worrying about cops and fiddling with my radar actually makes me a much more dangerous driver than I need to be. I try very hard to eliminate all distractions and just focus on the road and the other cars and the driving, but such a huge amount of my attention has to be spent keeping my eye out for cops or responding to radar blips. It's also a myth that tickets make people safer ; boy racers don't slow down until they have enough tickets to lose their license. I never slowed down when I was young and paying $6000/year in insurance. The penalty is just not high enough, and not predictable enough.

I'm a much safer driver now, but the reason is crashing a number of times. None of the crashes was due to me speeding, they were largely due to things out of my control, such as bad road condition problems or old ladies running red lights. The thing that really did it though was my cycling crash, which made me realize how absolutely fucking shitty it is to get injured and have to live the rest of your life with a damaged body.

3 comments:

Brian said...

4. Replace a porsche with a more pedestrian car. :)

sly-id said...

5. Don't over speed :)

Oh, right...

Aaron said...

Speeding in the rain can backfire. The one ticket I've ever had was from a motorcycle cop in (albeit light) rain, for like 67 in a 60. I swear he just wrote me the ticket so he could hit his quota and go back to the office.

old rants