Traffic Radar procedure question

[CaptainTom]

I was out and about yesterday in my neighborhood and watched a Ft. Worth PD cruiser working radar just up the street from my house. I had a chance to observe him for about 15 minutes.

He had a hand held radar unit. He was facing the oncoming traffic.
He scanned the oncoming cars normally, but when a car was coming up from behind, he would put the radar unit very close to the side view mirror and shoot the car using the mirror. He did not point the unit directly at the car, but was 180 degrees in the other direction.

Is this accurate? Enforceable? Ethical ?

He did not pull anyone over, because he was likely being given up by cars warning each other.

I know a bunch of LEO's are on here, so it would be better to get an informed answer than the usual plethora of opinions.

[Bob_S]

"Lasers"

[Murph]

Been so long since I did the Radar certification, I can't recall. He might have been using the new Ladar (Laser based Radar). And I have never used a handheld radar gun, so I don't know.

[Marv800]

LIDAR > Speeders

[CallMeAl]

There are a couple of possibilities. One, he has two radar heads. One mounted in the rear deck and one removeable head in the front. The front head, often looks like the stereotypical "gun," and can be mounted for use in moving radar or removed and handheld. When running radar like that, I would often rest the radar on the mirror when not actively using it. That could be it.

However, it is possible to get a reading by "shooting" the vehicle in the rearview mirror. I'm not sure how accurate it is and I definitely wouldn't stop a vehicle based on it! I haven't seen anyone try to prove it in court, but it is definitely outside the guidelines of normal and accepted training.

That being said, I would say that he was probably just checking to see if the vehicle was speeding up just out of curiosity.

Hope that helps.

[CaptainTom]

I also think he was just experimenting with it. He was definitely pointing it into the outside mirror. He would only do it when a car approached from his rear.
I watched for about 15 minutes or so. I live in a far fetched corner of the city where you have to go through two other burgs just to get here.
We don't see many FWPD here because we are surrounded by another city.

[janikphoto]

In theory, it shouldn't affect the end result. I'm not LEO, but I understand physics. The speed is determined by calculating the difference between two beams within a preset amount of time. Both beams would've been shot through the mirror, so there would be no variance.

Now, if it doesn't follow normal, written procedure, a judge could throw out the case on that basis... I know he can dismiss a radar reading if the unit is past it's scheduled maintenance point as well.

[CallMeAl]

Originally Posted by janikphoto

I know he can dismiss a radar reading if the unit is past it's scheduled maintenance point as well.

This wasn't asked, but I thought I'd throw it out there for information purposes.

The radar units are routinely calibrated and checked. Since tickets from radar/speed enforcement contribute greatly to a city's budget, they seldom skimp on this area. If you intend to challenge a ticket based on the maintenance records of the radar unit and/or it's calibration, be prepared to show the maintenance records / record of calibration for your vehicle. Usually, people say they weren't going the accused speed based on their speedometer. I don't know about you, but I've never had my speedometer checked or calibrated. Keep that in mind if you intend to use that defense.

[richardsfault]

I wonder if it was more modern multi-directional unit intentionally placed in an "old school" looking housing?

I don't see how such a stealth procedure would be illegal anymore than hiding behind an obstruction.

At least the officer wasn't out looking for photographers to harass

[CaptainTom]

Originally Posted by richardsfault

I wonder if it was more modern multi-directional unit intentionally placed in an "old school" looking housing?

I don't see how such a stealth procedure would be illegal anymore than hiding behind an obstruction.

At least the officer wasn't out looking for photographers to harass

I'm still not convinced that the pulse doesn't get distorted somehow when it reads a mirror image instead of a direct read. Maybe they need a note on the mirror "Things in mirror may look faster than they are."

Does the reflected reading make "cosine error" better or worse ?

[jeffro20]

Whatever the case may be.....just beware if you travel I-20 (820 S. Fort Worth) along the Wichita Exit to I-35. They radar that stretch DAILY and I see somebody pulled over EVERY DAY. They work that stretch hard.

[hooligan]

You can use a traditional RADAR, k band, ka band....and use the reflective ability of the mirror to get a speed off of a car behind you. All LIDAR (lazer) units have some kind of red dot aiming device that you must look through. I have never even tried the lazer in a mirror. i do know that the type we use, you can not shoot through glass.

Back in the day when all we had were hand helds, we used to use the mirror all the time. We were even shown in training with a second unit that the speed reading was accurate. It is not useful for lots of traffic behind you unless there is one obviously faster vehicle in the front of the pack.

[CallMeAl]

Originally Posted by CaptainTom

Does the reflected reading make "cosine error" better or worse ?

It's not a "Cosine Error," but rather a "Cosine Effect." An error would imply an irregularity. It's an effect because it's a fact based on a mathmatical formula.

For those that don't know, the cosine effect relates to the accuracy of the speed reading based on the degree of angle between the target vehicle and the radar. To be accurate, the angle between the two needs to be as close to straight on as possible. There is an allowable variance ( I think it's 7-10 degrees or so--It's been a few years since I was in patrol). Beyond that variance, the speed reading is not accurate and shows a slower speed which benefits the violator. However, as the officer, you are stating how fast someone is traveling...not that they were traveling "at least this fast."

For example, if an officer is sitting on the side of the road and "shoots" a vehicle in the middle lane, the angle between the two (taget and radar) is at a less angle if they are 150 feet apart as opposed to 75 feet apart.

Does that make sense?

[richardsfault]

Originally Posted by CallMeAl

It's not a "Cosine Error," but rather a "Cosine Does that make sense?

Now you're going off on a tangent.

[Jeff_Green]

But the side mirror is not completely flat, is it? Hence the "objects in mirror" warning. Would not that convex give you the possibility of an inaccurate reading?