(OT) Traffic Speed Detecting Signs

[Paintedcow]

Our town recently got one of those Traffic Speed Detecting Signs, that tell you how fast you're going. I've always wondered how they work, and why they dont detect cars going the opposite direction.(I assume they work on radar). I also noticed that they only have TWO digits. Therefore, if you exceed 99mph, what does the sign do?

Last night I was in a convenvience store, when one of the local cops walked in. That was my chance to ask him what happens if someone exceeds

99mph. His reply was "I'll give you a speeding ticket". I laughed and said "that's what I thought you'd say". Then I said, "besides the ticket, what would the sign do?" He said he never tried it, so he dont know.

If a cop dont know, who does? I'm wondering if they go back to zero, or just keep showing 99?????

[DerbyDad03]

Obviously your town doesn't have a Idiot Ordinance. If they did, the cops would have arrested you on the spot.

[Ed Pawlowski]

That was probably a wrong answer too. At that speed you'd probably be arrested and charged with a series of reckless endangerment type charges. In CT if you are more than 20 over, off to the pokey.

[Frank]

He's mixing the sign and physical presence of cop. There are a couple of signs I frequently go through here and they blink off when your car has passed. They do not keep a record of your car and speed.

In Europe over 25 years ago we were told that trucks were required to have a recorded record of their trip and when cops pulled them over would check the record and could give them a speeding ticket even though they exceeded the speed hours ago.

One day with gps's and computers recording they could do this to anybody.

[Pat]

Yes, they work on radar. Cars going the opposite direction DO get detected, but they show up as going a negative speed. The built-in software just ignores those signals and displays only positive speeds.

[Unquestionably Confused]

Interesting.

Seems obvious that they must employ a unique radar frequency as oftentimes my Valentine One (a great radar detector) doesn't utter a sound even though it's set to report ALL threats.

The silent treatment occurs with a fair number of the portable "Speed Alert" trailers the police move around to provide a courtesy warning to motorists as well.

[DerbyDad03]

So I want to speed past one of those set-ups I should drive in reverse?

[DerbyDad03]

...or they show 3 digits.

[Taxed and Spent]

no, that is how you turn back your odometer before you sell the car.

[Micky]

It fires a rocket.

>

[Micky]

That's the best kind.

[cowabunga dude]

Those speed detectors always show my vehicle is going 3 mph slower than my speedometer.

[ChairMan]

+10 and bet the cop had a good laugh later telling his fellow cops about the idiot at the store

[DerbyDad03]

Have you compared your speedometer with a GPS or GPS app on a smartphone?

When you use the words "Those speed detectors always", I have to suspect the one thing that is consistent in every case: Your speedometer. I'd find it hard to believe that every one of those detectors is off by 3 MPH.

Somehow you'd think that they'd have fixed that by now...

[James Wilkinson]

Because your speedometer (like in most cars) is shit. Compare it with your GPS it should be dead on.

[James Wilkinson]

Those detectors are shit, I got too many false positives from other things that use the same frequencies (apparently tractor and taxi radios?!). The best thing to use is a GPS which has all the spots they put cameras (including mobile ones) in its database.

[James Wilkinson]

If it's aimed along this side of the road, it shouldn't see cars on the other side. Otherwise what happens if there's cars going both ways at once?

[FromTheRafters]

He was probably at the 99 cent store trying to hand the clerk a dollar just to see what would happen.

[DerbyDad03]

Mr. MaCaw,

It could be tires if he is running something other than the OEM size.

[Paintedcow]

If there are a line of cars approaching the sign, the numbers tend to jump around quite a bit. So which car is it sensing? (Of course a line of cars are all doing roughly the same speed).