speed accuracy

[mike_d]

I've checked my speed using a stop watch and the marker posts on the motorway. The speedo always overreads. If you have a trip computer in the car this is often much more accurate, zero it, drive at a steady speed and see the difference between its average speed and the speedo's reading! Another one is the roadside readings you see in some areas, "Your Speed XXmph", always less than the reading on your speedo.

Mike

[JLee]

[stevex9]

Hi all.

This is amazing.All these different answers, including what the police do too.

Could i just set the record straight - cop cars don't have to have, nor do they have their speedos/radar checked or calibrated everyday and they cannot restrict you driving if your tyres are over inflated.

There are certain times when they check their speedos and radar and they can place a prohibition order on your car for certain reasons.

Be careful not to take too many of the above answers as gospel...You may get arrested and thrown in jail for life for having a dirty windscreen...heaven forbid..(sorry people - only JOKING..)

Cheers

(A real plod)

stevex9

[alix776]

or for stopping on the hard shoulder of the m6 to ask directions

seriously the calibrated speedo of traffic does have to be checked though not everyday I think its similar rules as us with tachgragh which have to be check at 2 and 6 year intervals though the check periods may be shorter for police cars that are like to be doing speed enforcemt the same is for radar gun the calibration I believe and may not be gosspel is the if a radar check is setup then it calibration of the gun must be checked with a poilce veihcle that has a calibrated speedo and car reg number mark in hand books

steve if I'm wrong anywhere here please correct me
slighty off topic

back on topic local to us we have rader speed sign that flags up the speed of the approching car my car shows 35 when the gps and sign shows 30
the thing to bear in mind is the gps on flat road at a steady speed gps is accuturate to 0.01 mph going up or down hill or turn corners will reduce the accueacy the trick is not to speed at the end of the day

_________________
currently using aponia truck navigation on windows phone. Good bye IOS don't let the door hit you on the way out .

Oh the joys of being a courier.
device Lumia 950 xl

[JLee]

There's not much I can't found out using google but I'm really struggling to find out what the distance is between the 2 white squares on the road used by traffic cops. Please someone tell me so I can use these to check the accuracy of my speedo.

[alix776]

the way to do it is to get the speedo calibrated by a vosa approved station
_________________
currently using aponia truck navigation on windows phone. Good bye IOS don't let the door hit you on the way out .

Oh the joys of being a courier.
device Lumia 950 xl

[Skippy]

[delboy0754]

[stevex9]

Hello again.

Ok, let me try to answer a few of the above.

Firstly - yes i am a cop and traffic cop, an approved driving instructor (ADi),i train people to be ADI's, i am an Advanced police driving instructor and a RoSPA driving examiner, most of this for the last 17 years.

The main thing here is the speeding element. DON'T do it and you won't have a problem.

In relation to what vehicle manufacturers do, i cannot say. In relation to what the police do i can say. I can only speak here from my own experience within my own force and the policies they implement.

A lot, but not all police vehicles are calibrated and have a certificate number displayed on the speedo. This is done by a recognised body and can be used as evidence in court.

Other vehicles that do not have this may not be as accurate. therefore if you are reported for speeding by a vehicle without a calibrated speedo then it would only be on the estimation of the officer and the speedo reading would be used as a back up.

In relation to the white squares on the road surface, i think you will find that these are placed here by the local Highways Authority for reasons unknown. You can check with them.

In certain locations there are 1 mile markers placed on the road. Sometimes stripes on pamposts or on the central reservation on a dual carriageway. These are tested and set at 1 mile.
What you need to do is get a stop watch and travel between the 2 posts at 60mph, start the watch at the first one and stop it at the second.Your reading should be one minute.

Police vehicles can do this at the start and finish of their shift or as soon as practicable after reporting somebody for speeding. The stop watch used by police is also calibrated - so be mindful of the one you use.

These readings may also be used in evidence.

In relation to a speed gun, or static speed camera, the normal practice is for a vehicle with a calibrated speedo to drive through the beam at 30mph to check its accuracy.

I hope some of this has helped in answering your comments.

Cheers

Stevex9

[Andy_P]

[stevex9]

Hi

Sorry Andy, i put static, i meant mobile, i.e the ones that pop up all over the place like in the back of a van..

I believe the static ones are calibrated seperately.

Cheers

Stevex9

[stevex9]

Hi (Delboy)

I have checked the two links you mention and i have to say that neither appear to be official websites of any kind. They seem to be 'fansites' or 'homemade' websites.

They do not refer to any reputable body to support what they say. I did not read them in full, but what i did read, especially on the second one show a number of inaccuracies or phrases that are not worded correctly.

It would be interesting to know if West Mids Police have authorised the use of teir Logo on the website. It is unusual for the police to associate themselves with things like this.

I think you have done exactly the right thing by trying to evidence your views, but i also think, unfortunately, you have ended up on sites that are not that accurate.

These forums are good fun aren't they....

Cheers

Stevex9

[alix776]

thansks for putting that up steve interseting stuff
_________________
currently using aponia truck navigation on windows phone. Good bye IOS don't let the door hit you on the way out .

Oh the joys of being a courier.
device Lumia 950 xl

[Unplugged]

Near to me theres one of those stupid signs wich reports your speed and shows a smiley face if your under the limit.

Thats seems to be spot on with what my TomTom displays.

Also some cameras dont have radars Truevelos for example use the good old speed distance time formular.

Theres two sensors in the road before the white lines and they time how long between one press and the other and then calculate your speed.

[tangiers]

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