Motorists face 'zero tolerance' approach to speeding on the motorways

[unixman]

...This is it (knew I had a pic of it). I defy anyone to tell 33 mph (legal) from 34 mph (not legal) on that! I'm not denying I wasn't speeding, I was.

From the pic, 30mph is not clear enough. On many UK cars it is marked in red but even then the clarity varies. The problem is that manufacturers have made speedos progressively smaller over the years, and speed ranges to be covered have increased. Figures every 10 mph used to be the norm, now it is every 20. Unfortunately that means that 30 and 70 do not actually appear as numbers. It is an issue, as stek's photo shows. Digital readout helps.

[NickFitz]

Car speedos (unless they are GPS based) will also vary due to tyre pressure (which is linked to the temperature according to Robert Boyle) and the tyre/wheel size. As the tread wears down the speedo will read higher, if the tyre is under-inflated, the speedo will read higher. Basically, if the overall tyre+wheel diameter is not as per when the car was calibrated, then the speedo will read wrong.

But the variations due to those factors are so small as to be negligible.

[SpontaneousOrder]

But the variations due to those factors are so small as to be negligible.

A quick calculation on a 22 inch wheel (including tyre) makes it about 0.28 mph under-read if you manage to get that wheel up in diameter by 2.5 mm, at 60 mph.

[stek]

Presumably GPS also won't be accurate enough for a zero tolerance policy when going up or down hill.

Yeah and my car was an auto - at the place I was done (camera van) it was a steep hill and i reckon it got me when the auto box hunted and changed down with a momentary increase in speed.

Honest Guv, it was the autobox and the tiny numbers what done me Officer.....

[OwlHoot]

I've been watching the time it takes me to get home to Devon each week under different road conditions and circumstances.

Overall, the difference in journey time between me following the speed limit all the way, or moderately exceeding the speed limit where reasonable, is negligible.

There are so many obstacles on the journey, roundabouts, single-carriageway bottlenecks, traffic lights etc, that there is absolutely no point whatsoever in speeding and risking the points.

I suspect most journeys over any significant distance would be the same.

That's certainly true if much of your journey is on A roads. But if like me it is mostly on motorways, and the traffic is OK with not too many roadworks, then I can save anything up to an hour toeing it a bit in the fast lane when safe.

Out of interest, roughly where do you travel from and to? I am also based in Devon, near Tiverton, and do a round trip there and back from Cambridge each week. So it is mostly motorways and the A361 (North Devon Link road). On friday evenings the journey down there takes typically 5 hours; but late on sunday evenings, starting at about 9pm, I can do it door to door in 3.5 hours.

[Chuck]

Out of interest, roughly where do you travel from and to? I am also based in Devon, near Tiverton, and do a round trip there and back from Cambridge each week. So it is mostly motorways and the A361 (North Devon Link road). On friday evenings the journey down there takes typically 5 hours; but late on sunday evenings, starting at about 9pm, I can do it door to door in 3.5 hours.

Not far from you. I'm near Honiton. I use A303-M3-A316 to/from weekday home in Twickenham. Normal journey is c2:35, although Glastonbury, solstice or bank holiday weekends push that up to 4 hours+.

I travel down on a Thursday to avoid the Friday crush and WFH on the Friday.

[darmstadt]

Yeah and my car was an auto - at the place I was done (camera van) it was a steep hill and i reckon it got me when the auto box hunted and changed down with a momentary increase in speed.

Honest Guv, it was the autobox and the tiny numbers what done me Officer.....

I have James Bond numberplates just in case although I haven't actually got blitzed for speeding in around 15 years and I drive a lot and a lot of that is fast: