realfresh

Hello all, I was just wondering about radar guns in cop cars? You can't really aim them right? i.e. a laser can pinpoint an exact car...but as far as radar guns go, you can't tell (unless one car is obviously going faster) which car gave the reading right?



Thanks in advance

fant0m_TL

radars are inaccurate... lasers are dead on... but like u said... if u the only car around, it will be easy to tell ...

they are putting the old radar guns in the roadside speed indicators... i tested it once... did 85 past it... reading "caught" me at 62.....

some departments still use radar... but more and more are going to laser now.

realfresh

yeah, I've noticed that

buhhbuhh

radar are quite accurate, it will usually give the speed of the bigger vehicle, state patrol here in WA use radar but i know other states laser is more popular

mrproul

what i don't get is pacing the only reason a cop say's they got the MPH from pacing is when i have asked to see the radar/laser gun but i have yet to see the actual MPH's. it is all BS.

Mrproul

fant0m_TL

yeah... they can only pace you when they are within i think 15 feet.... and they cant have radar on while doing it... because (this was tested on myth busters and my physics class) a radar cant accuratly give a speed when it is in motion.

i talked to my dad about it - hes been a cop for 20+years - he said they have laser utilities now that calculate the policecar and then the car they are shooting and find out the speed that way... so watch out for that as well.

avs007

I've seen some of those setups... They can be inaccurate as well, becuase it "measures" the speed of the police car, rather than tying into the speedo, and using the actual speed... Measuring the speed of the police car is inaccurate, becuase it can inadvertantly use an object in motion as a reference point.

Anyways...

Because the range of radar can be outside the visible range, you can't really use the, "if you're the only car around" reasoning...

My wife got a ticket once, and I busted out the video recorder, and showed how easy it was to fool the radar going down the hill by my house. Was pretty easy to get the ticket dropped.

I basically showed my speed as being 35 going down the hill, but showed the radar showing my speed as being 50, when there were no other cars in "close proximity" to the radar. (I was like 100 ft in front of the radar, I had another car about 1/2 mile or more away, at the top of the hill going 50. I was able to easily get the radar to show 35, flip back and forth between 35 and 50, and then read a solid 50. I also got it to show 35, and then accelerate to 50, even though I maintained a steady speed.

iceycherry

radar is accurate as hell if it is laser

fant0m_TL

im really not trying to sound like an @$$... so im sorry if i come across like that i honestly am not....

but that didnt make sense at all...

radar is radar, and laser is laser... same concept, different beams/range

avs007

The one problem with laser is what it's using as reference points. Since laser is invisible, you can't really be 100% sure what it's using...

For example, if in the 2 samples, it used the windshield in sample one, and the front plate in sample 2, it'll mis-calculate your speed to be faster than what it really is.

This is essentially how in England for example, they threw out laser, becuase they were able to show the courtroom wall was moving at 25mph.

Laser can also be easily reflected/refracted by heat, rain, etc. Since laser is invisible you can't really be absolutely 100% certain of your aim. Especially at greater distances and such.

avs007

Actually, they are completely different in concept.

RADAR = Radio Detection and Ranging
LASER = Light Amplification by Stimulated Emitted Radiation

You might be thinkng of RADAR and LIDAR, but they are still completely different.

RADAR measures speed based on doppler shift.
LIDAR measures speed by calculating velocity based on the change in distance measured over time.

trancemission

This is Off Topic and needs to be posted in Car Talk.