How does police radar work?

Wayne Maybury · #1 (**permalink**) 09-28-2009, 02:01 PM

I have had my share of speeding tickets, especially when I was much younger. I never complained since I knew I was guilty. However I got a ticket 2 weeks ago that I feel was totally wrong.

Without going into a long explanation, I was being passed by a pickup truck who was going faster than me just as we got into range of a police radar trap. Instead of stopping the pickup, the officer stopped me instead. The officer was inside the car with the radar mounted on the outside of the rear left side window. I have to assume that he didn't see the pickup in his mirror. When he pulled me over, I explained that it was the pickup speeding, not me. His answer was "the radar told me it was you that was speeding". Can modern radar specify which vehicle it has spotted?

I have pleaded not guilty and I will have to go to traffic court soon. This was not a hand held radar gun, this was a window mounted unit. My understanding is that this type of radar unit will pick up the speed of the fastest moving vehicle but it really cannot state which vehicle unless there is just one there. Can anyone tell me if that is correct?

I think that the officer simply made an error but I do not want to make a false statement in court. Any help would be appreciated. By the way I was following several other cars all in the right lane so I couldn't possibly be going faster than them or I would have run over them. The pickup passed me and was about to pass the other cars when he spotted the police car at which time he pulled in the opening in front of me.

Wayne

bomelia · #2 (**permalink**) 09-28-2009, 04:08 PM

Were you over the speed limit?

cobra de capell · #3 (**permalink**) 09-28-2009, 04:12 PM

http://www.radarguns.com/how-radar-guns-work.html

You don't have a Traffic School option is Canada?

Bobcat · #4 (**permalink**) 09-28-2009, 04:27 PM

I`ve been told that police radar picks out the strongest signal ... not always the closest object . For example , if a semi was 50 yards behind you , the unit would read the trucks speed and not your car`s . If I understand radar correctly , it cannot specify which vehicle is speeding ( laser can ) ... unless you are the only car on the road . For that reason , if you are the lead vehicle , you are screwed . From what you say , he probably wasn`t paying attention and looked up when the alert on the unit went off and saw you after the truck passed . I had a friend who was a GA trooper and he said they relied on the unit alerting them when a vehicle was over the trigger point ... then it was up to him to figure which vehicle it was .
Don`t know how it is in Canada , but the police have to be able to prove the unit is properly registered and calibrated before each shift . If not , the ticket can usually be fought successfully . You might try Valentine`s and Cincinnati Microwave`s ( radar detectors ) web sites for more info .
Good luck .

dcdoug · #5 (**permalink**) 09-28-2009, 05:39 PM

The beam spreads as distance increases so you are "painting" a pretty good area if you were a reasonable distance from the cop. Could have easily picked up on another car. A laser doesn't diffuse very much, so it is much more precise.

DAVID GAGNARD · #6 (**permalink**) 09-28-2009, 06:03 PM

Quote:

I`ve been told that police radar picks out the strongest signal ... not always the closest object . For example , if a semi was 50 yards behind you , the unit would read the trucks speed and not your car`s .

Correct according to a state trooper buddy of mine....he told me a small to midsize car could be passing an 18 wheeler on a 4-lane road going a lot faster and his radar will pick up the largest obect of the two, regardless of their speed.......the radar unit reflects back it's signal to the unit and reflects back the largest object the "radar waves" hit in it's path..... lasers are a different story....

I asked him when there are 3 or 4 or more cars in a "caravan" speeding, which do you get????? He said it will usually pick up the first in line providing there are all similar in size, but not always, I asked which one do you stop, he said the first one to pull over to his lights!!!!!!!!!!!!!!!!!!!!!!!!!!

David

Wayne Maybury · #7 (**permalink**) 09-28-2009, 07:50 PM

To answer a couple of the remarks / questions.

Yes I was speeding but not nearly at the speed he said. The police car was just inside a construction zone where the speed was decreased from 100 kmh (65 mph) to 70 kmh (45mph). When I entered the zone I was decreasing my speed from about 110 to eventually 75. I believe that I was doing 90 to 95 kmh when I first entered the zone. He ticketed me for 114 kmh which is higher than the speed I was travelling in the 100 zone.

I was following 3 or 4 smaller cars with my Explorer but I was being passed by a duel wheel crew cab Dodge pickup which is definitely bigger than my Explorer. I'm not even sure the pickup was doing 114. The pickup did pass me then cut in front of me once he saw the police car. He knew that he had been caught as he kept looking in his mirrors waiting for the cop to pull him over.

First to pull over once the flashers are on is a good one. Well that is interesting. As I said there were 3 or 4 cars ahead of me, then the pickup pulled in directly in front of me and the police car began following directly behind me. We continued on that way for about a mile at which time I had to take an exit but all of the other vehicles kept going straight. The police car follwed me and only turned on his flashers once I had taken the exit. I had no choice but to stop and everyone else was long gone by then.

Wayne

bomelia · #8 (**permalink**) 09-28-2009, 11:03 PM

Wayne,

I think you are SOL. I once got caught in a "trap" where about 10 cars were all going over the limit (in town, rush hour). I got picked out of the middle, no one else. When I asked about that, the cop said it was a judgment call. Sucks. But "conciousness of guilt" will trip you up in court unless you are a very good actor and/or liar (I am neither, though I have tried). The judge will ask you if you were knowingly speeding, in any case. Now, what are you going to say? "Well yeah, but the bigger truck was going faster!" Remember, you will be under oath, and that is a powerful thing to deal with.

You'd be better off to hire a lawyer to do the dirty work (maybe Jamo can do it) now that you are in this deep, or beg out of going to court. You are going to end up having to pay the ticket and the court costs. Not to mention any other crap the judge might throw at you for wasting his time.

If you were not speeding, then I would most def go to court on principle alone. Lack of "consciousness of guilt" would really work in your favor.

I hope you do not take this as snide remarks. I am speaking from experience.

Most of all, I sincerely hope I am wrong.

Mike

Quote:

Originally Posted by Wayne Maybury

To answer a couple of the remarks / questions.

Yes I was speeding but not nearly at the speed he said. The police car was just inside a construction zone where the speed was decreased from 100 kmh (65 mph) to 70 kmh (45mph). When I entered the zone I was decreasing my speed from about 110 to eventually 75. I believe that I was doing 90 to 95 kmh when I first entered the zone. He ticketed me for 114 kmh which is higher than the speed I was travelling in the 100 zone.

I was following 3 or 4 smaller cars with my Explorer but I was being passed by a duel wheel crew cab Dodge pickup which is definitely bigger than my Explorer. I'm not even sure the pickup was doing 114. The pickup did pass me then cut in front of me once he saw the police car. He knew that he had been caught as he kept looking in his mirrors waiting for the cop to pull him over.

First to pull over once the flashers are on is a good one. Well that is interesting. As I said there were 3 or 4 cars ahead of me, then the pickup pulled in directly in front of me and the police car began following directly behind me. We continued on that way for about a mile at which time I had to take an exit but all of the other vehicles kept going straight. The police car follwed me and only turned on his flashers once I had taken the exit. I had no choice but to stop and everyone else was long gone by then.

Wayne

Wayne Maybury · #9 (**permalink**) 09-29-2009, 05:45 AM

Mike

Thanks for the candid remarks. I am not insulted at all. I plan on pleading not guilty to doing 114 in a 70 zone. I am prepared to plead guilty to doing 90 or 95 in the 70 zone. The ticket is $249 and 3 points. I figure that the court costs will be another $30 or $40 if the judge thinks that I have no case. Of course I am also hoping that the police officer doesn't show up for court.

I will let you know how I make out, in a few weeks. The court date hasn't been set yet.

Wayne

Ron61 · #10 (**permalink**) 09-29-2009, 06:03 AM

Wayne,

Do they set up those road side radars up there from time to time? If they do, watch it and especially if there is other traffic around you and you may be surprised. I was trying to see how accurate my speedometer was and one of them kept jumping from one speed to another and I was the only vehicle close to it. I knew that I wasn't doing 60 MPH as I was in a 40 zone and finally figured it must be picking up cars that were almost a block behind me. It would jump from 40 to 60 to something else and back and forth. They aren't exact as to correctness but give you a god idea of how fast you are going and are good to check your speed with.

Ron

Bill Bess · #11 (**permalink**) 09-29-2009, 06:40 AM

Hey, just write all these "possibilities for an in accurate radar reading and identifying the wrong vehicle" on a sign board and then go to court, politely state your case.
Don't fabricate a dump story that the judge has heard a million times before...just state your case and opinion.
No matter what the outcome, thank the court for their time, if it's a bad outcome...tuck your tail between your legs and go pay the ticket.
Perhaps being more aware of your surroundings and slowing up sooner will prevent getting "pinched " in the future.
Best of luck, Bill

Bobcat · #12 (**permalink**) 09-29-2009, 08:09 AM

Wayne ... looks like what happened was that the radar picked up the strongest signal ... the duelie Dodge . When the cop looked up , he saw you in front of the smaller cars and assumed it was you he registered on . As Bomelia said , I think you are SOL . IMO the only thing you have to consider is whether you want to get a lawyer ... i.e. will this cause you to lose your license or have to pay a massive fine . Down here , the courts will take to police`s word over a civilian`s ... that`s just the way it works . You might try asking for the court date to be rescheduled , and have a good reason . Sometimes the cop won`t show up for the second ( or third ) date .
Good Luck .

Bob

Dan40 · #13 (**permalink**) 09-29-2009, 08:59 AM

Think about this:

http://www.amazon.com/Ticket-Book-Ro...owViewpoints=1

Wayne Maybury · #14 (**permalink**) 09-29-2009, 02:26 PM

Bill, that is exactly how I plan on doing it. I am going to present the facts as I see them and state that I believe that the office made an error based on the fact that he probably did not see the pickup from his position (his car was well hidden so all he could do was to look at the small side mirror to see what was happening behind him). I will be polite and factual.

Bobcat, I have all 15 points and this could cost me 3 points so I would be left with 12 points. The fine is $249. Neither will break me but what really bothers me is that the officer stopped the wrong guy. The driver of the pickup knew that he had been caught and he must still be laughing about the officer stopping me instead of him.

I spoke to a friend earlier today and he told me that I will probably not get a court date for at least 4 or 5 months. I am going to write down the facts as I understand them so that I do not get confused between now and the time I get to court.

Wayne

bomelia · #15 (**permalink**) 09-29-2009, 10:29 PM

Wayne, thats the problem. The officer did not make an error. You admitted you were over the limit. That has psychological implications for you. The fact that the officer did not catch the one going the MOST over the limit is irrelevant. I have played this one out in my own mind many times. Chances are very good you will never know how many other folks (if any) got a ticket in the exact same situation when you were the worst violator. If you know for a fact that you were not speeding, then hell yeah, I would go to court and raise a holy stink on principle alone. It might not do me any good and it might cost me more, but knowing I am right will possibly shine through and earn me a victory. However, you are putting yourself into a situation where you may very well have to cast your principles aside in order to prove your point, and that will shine through as well.

Better to ask mercy from the court and permission to take a "safe driving" course (to get out of the points) then to argue that someone was breaking the law more than you were. It is after all, about the points, right? You could say "yes sir, I was in a moving parking lot that on average was above the limit. I was going with the flow. I think what most likely triggered the radar was a this big duelie passing me at the same exact moment. Unfortunatley for me, I got caught, and fortunately for him, he did not. All I am doing here today is asking for mercy and access to a safe driving course at my expenese to mitigate points on my record... I will gladly pay any assessed fees as I was no more better than the duelie going by me at 114Km/hr"

I think you will find that in another form in "How to win friends and influence others"

Mike

SPF2245 · #16 (**permalink**) 09-30-2009, 02:20 AM

Both my in car (MPH) and hand held radar (Genesis) allow me to target the largest target (or strongest target) and/or largest and fastest target. Both are directional so I can choose to ignore vehicles traveling in either direction (ie opposite direction traffic). My mobile will also allow for same direction (in front or behind me) moving targets while I'm at speed. Regardless of the operation, I am required to make a visual estimation prior to locking in the speed on radar in order to eliminate your arguement (does it always happen first...um no). Now, are there guys who work off the reading purely...yep, and it's wrong. State your case, ask the officer if he had made his visual estimate, quality of tone emitted by the unit at the time of lock (this can cause "reasonable doubt"), and distance he made his observation and even bring in his estimate of the truck (supporting your case his unit was tracking that vehicles speed). Good luck.

As for the arguement about signs or surfaces reflecting the signal, this does happen, but the audible signal tells the opperator it's occuring by providing a poor quality sound during operation verses a solid sound with a good lock. Now, if it's LIDAR...your screwed, there is no escape and it's what I love using most because of it's accuracy (you target a specific vehicle with an Aim Point style retical), and it provides speed and distance at lock. Pretty cool and it eliminates these problems.

trularin · #17 (**permalink**) 09-30-2009, 05:27 AM

Radar is a targeted wave at a designated frequency. The designer knows how long each wave is and based on emission and reflection times, the speed can be determined.

Here is the problem: it is a line of sight device. Any object that reflects the wave has to be in the line of sight and there actually is no way to tell what object is providing the reflection unless you have a differential imaging system.

Hope this helps.

Wayne Maybury · #18 (**permalink**) 10-02-2009, 08:53 AM

Quote:

Originally Posted by SPF2245

Both my in car (MPH) and hand held radar (Genesis) allow me to target the largest target (or strongest target) and/or largest and fastest target. Both are directional so I can choose to ignore vehicles traveling in either direction (ie opposite direction traffic). My mobile will also allow for same direction (in front or behind me) moving targets while I'm at speed. Regardless of the operation, I am required to make a visual estimation prior to locking in the speed on radar in order to eliminate your arguement (does it always happen first...um no). Now, are there guys who work off the reading purely...yep, and it's wrong. State your case, ask the officer if he had made his visual estimate, quality of tone emitted by the unit at the time of lock (this can cause "reasonable doubt"), and distance he made his observation and even bring in his estimate of the truck (supporting your case his unit was tracking that vehicles speed). Good luck.

As for the arguement about signs or surfaces reflecting the signal, this does happen, but the audible signal tells the opperator it's occuring by providing a poor quality sound during operation verses a solid sound with a good lock. Now, if it's LIDAR...your screwed, there is no escape and it's what I love using most because of it's accuracy (you target a specific vehicle with an Aim Point style retical), and it provides speed and distance at lock. Pretty cool and it eliminates these problems.

Thanks, this is the information that I was looking for. The officer's car was very well hidden behind some construction equipment or material so while the traffic could not see police car, the officer could not really see the traffic except in his small outside left door mounted mirror. He was inside the car and was using a radar unit which was mounted on the outside of the left rear window. I think that the radar signal went off and he looked in his mirror and saw me when in fact it was the pickup that was actually setting off the radar. When he stopped me, I told him that it was the pickup that he should have stopped, not me. At that time he stated that "the radar told him that it was me speeding". This seemed to me to be a very strange comment by the officer. I want to repeat this comment in court but I do not want to look like an idiot either.

Mike, I have pleaded not guilty to doing 114 in a 70 zone, not that I wasn't speeding at all. I am quite willing to admit that I was doing 95 in the 70 zone (whether or not others were doing the same speed is irrelavent) and take my punishment. However, I feel that the officer missed the actual culprit as he probably didn't see him in his mirror. I cannot see any other explanation.

I will let you know how this eventually turns out once I get my court date.

Wayne

dcdoug · #19 (**permalink**) 10-02-2009, 09:13 AM

You should go back and take some pictures of his location and the construction equipment (if its still there) from the location of your car at the time you were radared to support your argument that he was unable to make a proper visual identification.

Wayne Maybury · #20 (**permalink**) 10-02-2009, 09:29 AM

Quote:

Originally Posted by dcdoug

You should go back and take some pictures of his location and the construction equipment (if its still there) from the location of your car at the time you were radared to support your argument that he was unable to make a proper visual identification.

Doug, I was going to do just that but they moved everything around a few days later so I cannot even be sure where the police car was at the time of the incident. This is a highway construction zone where they are building a new interchange so the detour is constantly being changed as the work progresses.

By the way, I go through this area every week and I now go no more than 75kmh in the 70 zone. Trucks, cars, and/or buses go flying by me like I am standing still. I especially like the area where it goes down to one lane as I then slow down to 70. Within seconds I am the leader of a big, unhappy parade.

There is no way that I am getting nailed there a second time.

Wayne