Speedo accuracy observations

The message from "Iain McLaren" contains these words:

If you want to check it, you might find the marker posts on the edge of the motorway are a better bet. They're 100m apart - so a passenger with a stopwatch can easily time you at a steady speed and calculate your actual speed to considerable accuracy.

you must have got a lucky one then most Vauxhalls of this vintage were upwards to 10/15% over reading they tested a corsa or something once and it had to reach 90 mph to get to

here's

My car has been off the raod since 2000, its a 77 Celica and im dreading all the speed cameras, i have a feeling the actual speed doesnt match the speedo.

Thought about asking traffic cops to flash me when i signal my speedo speed of say 30 in 30 zone.

but they'll be hiding in a hedge how will you spot them :)

I tried the above on a late night (early morning!) trip back from bristol up the M4.

With the Speedo showing bang on *ahem* 100mph the marker posts/stop watch showed I was doing 94mph. 2000 Focus Zetec on 195/60-15 tyres..

I couldnt be arsed to check it at a lower speed. Will check the Volvo at weekend if M4 to cardiff is quiet.

Tim..

i meant if i saw then in a cop car to ask, i know the rul of 10% over but i would really hate slowing to like 25 just to be safe.

Well my old Volvo was 10% out at all speeds. I was then shown an official Volvo service bulletin explaining that this was actually deliberate on Volvos part in the name of safety.

But this week I had a chance to check out my new one with the help of an acquaintance who has VASCAR fitted to his company car :-) My speedo seems to be spot on at 30, 50, 70 and 90 so I assume that Volvo have stopped doing this.

My Fiat Stilo Abarth reads spot-on at all speeds that I've tested it at, using an Origin Blue GPS camera detector, which has a GPS speedo built-in.

I was quite surprised to see an indicated 90MPH being exactly 90MPH on the GPS unit.

Is VASCAR the system that uses the single white stripes across the carriageway to measure the time to travel a known distance?

I know someone who knows someone who has the job of measuring these and has been known (so the story goes) to add a little to the official distance (100m?) to give people a sporting chance!

The message from "JULIAN HALES" contains these words:

Like I said - calibrate it against the marker posts on the motorway. Just needs a passenger who can use the stopwatch on their mobile and can handle a bit of simple arithmetic.

Thats for higher speeds, i was think more of 30, the M1 near me wouldnt be safe to do 30!

Yes it measures between 2 fixed points. In some areas there are white lines on the road, in others, white squares and where these don't exist, you can use bridges or anything else you want.

: I know someone who knows someone who has the job of measuring these and has : been known (so the story goes) to add a little to the official distance : (100m?) to give people a sporting chance!

I know a roads engineer, one of whose jobs was to oversee the installation of the white squares in the middle of the road which are used for speed measuring and also, apparently, for aerial surveying as known positions.

Just after he had had one painted, a lorry did a multipoint turn over it ... since the paint was wet, they ended up with about ten squares ..

Ian

The message from "JULIAN HALES" contains these words:

They have 'em on A-roads sometimes - pick a quiet one.

I once overtook a white-lining machine. My tyre tracks were visible for years!

Luckily it was quite an old car, so the white blobs stuck to it weren't much of a problem...

The message from "Ian Johnston" contains these words:

While we're on the subject - why are the roads of Wales covered with yellow double-ended crosses?

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About 10" long?

Or use the hard shoulder ;-)

Where abouts in Wales? Also, do they appear in any particular circumstances (e.g. at junctions or only at the sides of the carriageway)? I now live there and have not seen any. Mind you, the area I live in is so isolated that *any* road markings are unusual.

Working only on the info you have given so far, my best guess is that they mark small faults in the surface which will be rectified prior to re-gritting the road surface. This theory would be more likely if the crosses are only on lanes, rather than major roads (whatever they are ).

The message from Howard Neil contains these words:

Abosultely bloody everywhere - and not associated with junctions or bridges or anything I can spot - just on the road.