How accurate are speed indicator signs ?

Zubair11

Hi everyone
Just to comeback from Worksop via mosborough and travelled through two in Worksop the speed indicated my speedo was showing 2mph fast @ 30 mph ( actual 28 mph according to sat nav and the roadside speed indicator )
Going through Mosborough .The roadside speed indicator showed the speed at 29mph the same as my speedo but sat nav said 27mph . How accurate are these signs any one any ideas , thanks

Silver-Surfer_2

Zubair11 wrote: »

Hi everyone
Just to comeback from Worksop via mosborough and travelled through two in Worksop the speed indicated my speedo was showing 2mph fast @ 30 mph ( actual 28 mph according to sat nav and the roadside speed indicator )
Going through Mosborough .The roadside speed indicator showed the speed at 29mph the same as my speedo but sat nav said 27mph . How accurate are these signs any one any ideas , thanks

Well if your sat nav is accurate you have your answer.

bigadaj

They always seem pretty accurate to me, but a difference of 1-2 mph is effectively a rounding error. Speedos will generally be reading 10% above in any case.

Ebe_Scrooge

Zubair11 wrote: »

How accurate are these signs

Not very ! Not at all, in fact. Just last week, I was travelling through a small town that had a speed indicator sign. Nose-to-tail traffic. We're doing about 25 mph ( as indicated by my speedo, which I know is not accurate, so probably closer to 20 mph ? ). Anyhow, so we've got a line of traffic doing something between 25 or 30 mph, something like that. The speed indicator sign was rapidly flashing between a green "15 mph" and a red "58mph" sign as each car passed it. Obviously they don't have to be calibrated as they can't "issue" tickets, but it just goes to show - what a waste of time and money.

Strider590

TBH I used to take notice of these signs, but now I just completely ignore them.

There are two I pass every day, one in a 30 zone, one in a 50 zone and they'll flash their stupid little message even if i'm doing 25 or 45 respectively, which is around 22 and 40 on my cars speedo.

They're aiming to make drivers check their speedo, but all it's doing is causing drivers to brake, taking their attention off the road ahead whilst they look confused at their instruments and wonder if there's something wrong with their car, meanwhile the driver behind has to jab the brakes to avoid colliding with said confused individual.

They should be set more accurately to the speed limit, then people might actually take notice of them.

bod1467

The one's I've passed have generally been reasonably close to the intended limits.

Ebe_Scrooge wrote: »

Anyhow, so we've got a line of traffic doing something between 25 or 30 mph, something like that. The speed indicator sign was rapidly flashing between a green "15 mph" and a red "58mph" sign as each car passed it.

This was likely because the sensor couldn't get a fix on an individual vehicle. I've noticed the same (though not as extreme a difference) under similar circumstances on the sign at the eastern entrance to my town.

coffeehound

Silver-Surfer wrote: »

Well if your sat nav is accurate you have your answer.

Probably another thread, but is the speed indication on sat-navs reliable?

prowla

I tend to think they are pretty accurate.
There's a road in Kingston where they show a smiley face if you're within the speed limit, which I think is vaguely amusing...

BeenThroughItAll

Strider590 wrote: »

TBH I used to take notice of these signs, but now I just completely ignore them.

There are two I pass every day, one in a 30 zone, one in a 50 zone and they'll flash their stupid little message even if i'm doing 25 or 45 respectively, which is around 22 and 40 on my cars speedo.

So your car's speedo UNDER-reads?

reeac

I've noticed that there are two kinds of speed signs- those that display the local speed limit when you approach them even when you are within that limit and those that display your actual speed. I find the former slightly annoying but the latter interesting. The latter, from my observations, agree within around 1 mph. with the electronic speedos (and the satnavs.) on my two newer cars but show that the eddy current speedo on my 1958 car reads around 3 mph. high. A convenient calibration system.

Nilrem

Zubair11 wrote: »

Hi everyone
Just to comeback from Worksop via mosborough and travelled through two in Worksop the speed indicated my speedo was showing 2mph fast @ 30 mph ( actual 28 mph according to sat nav and the roadside speed indicator )
Going through Mosborough .The roadside speed indicator showed the speed at 29mph the same as my speedo but sat nav said 27mph . How accurate are these signs any one any ideas , thanks

Not very.

We had one near me that would flash up "30" at ever decreasing speeds, I think it got to the point where it would flash as you went past it at 15mph before it got taken down.
As it was on a residential road I had to drive down pretty much every time I went out it became a bit of a game if there was no other traffic to go past it at a different speed (up to the limit) every time to find out when it would stop the warning flashes.

It went from triggering at about 25mph indicated, to 15mph indicated over the space of 6 months.