Speedo Inaccuracy - Motorway Mileposts

Dec 13, 2004 9 Replies

I've got a speedo/trip both of which I suspect as being wrong, but not by the same amount. Can anybody tell me exactly how far apart those little blue/white marker posts are on the Motorway? I know they're numbered, but I need to know the distance so I can check this.



TIA



Alex


100m IIRC - maybe 100yds - they usually say how far to the next emergency telephone, and some also have a distance to it too

Si

On or around Mon, 13 Dec 2004 20:04:47 -0000, "Si K" enlightened us thusly:

telephones are ISTR a mile apart.

however, the markers have numbers on them in km and tenths, starting from one end of the m-way. so you can, in the slow lane, say, travel at 60 kph and have someone time between e.g. 173 and 174 km, and use that to work out how fast you were really going, if you get an answer significantly different to 1 minute. Likewise you can use 'em to check yer milometer.

100m

I don't think the normal ones have any distance information just the direction to the nearest phone. Phones are spaced at 1.5km (+/-10%) on normal motorways but going down to 1km on four lane.

From Google:

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Or find the "measured mile" that is normally near to the local traffic police HQ. They use it to check their speedos...

Its 100yds not 100m.

Stu

They are 100m apart, with a positioning tolerance of +/- 1m

The numbers are km (the top row of numbers) & tenths (the second row) from the start of the motorway.

Regards

Steve G

Alex wrote:

Better still look out for blue marker posts, normally on dual carriageway near police garages, these will be set 1 mile apart and used to calibrate speedo's etc.

Tony

Didn't I just say that? B-) Though of the 3 or 4 measured miles I know of the markers have all been different.

The small marker posts on motorways really are 100m apart not 100yds, the measure the distance of that point from the start of the motorway in km and 1/10ths of a km. ie 100m.

On Mon, 13 Dec 2004 13:36:07 -0600, Alex wrote (in article ):

I believe because of the way the laws governing speedometers are written it will be off. Car and Driver Mag had a good article explaining the difference between American made and European made cars.

The American cars have to be plus or minus two percent. The European cars have to read high. Everybody I know with a European car will read 75 MPH at a true 70. That is true of my 96 disco as well. This is checked both with GPS and Mile markers.

The Odometer should be correct since at least in the U.S. it goes on the title and must be accurate. Also for the warranty. Hud

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