May Had Been Caught

[markelvin]

Driving from Poole to Dorchester on Saturday at about 90mph, on the entry slip of the OPPOSITE side of the dual carrigeway there was a silver Volvo parked up with a BiB with the window open pointing his "device" out of it.

I'm hoping he was doing the opposite carrigeways.

Edited by markelvin on Monday 18th December 09:53

[supermono]

I'm fairly certain they're not allowed to operate across the central divider. Besides the angle would be such that an accurate reading couldn't be guaranteed (yeah, like it ever can with "dodgyscopes". Not only that but your numberplate might well have been obscured by the armco.

Reckon you probably got away with your death defying 90mph lunatic moment this time

SM

[simpo two]

IIRC there's something called the cosine effect which affects accuracy at angles, but I don't know how it's applied.

What he forgot was the classic line 'I was just seeing what it would do', which has been proved to work up to 170mph...

[supermono]

The cosine effect is an adjustment to actual distance compared with the measured distance travelled. Imagine a right angled triangle formed between you and plod, the line perpendicular to plod across the road and your direction of travel. If he measures your distance (the hypotenuse) changing by dx metres, the actual difference covered will be something like dx cos theta, where theta is the (constantly changing) angle between the road line and the hypotenuse.

SM

[simpo two]

He'd need to know the angles to calculate the speed, no?

[supermono]

Well he'll know three sides of the right angled triangle at two different points so I'm reckoning he could work out the two angles too and take the average speed between both?

Although saying that, you know that the speed measured will always be lower than the actual speed (hypotenuse is by definition longer than the other two sides) so I've always been puzzled why they can't say at least x mph. Puzzled and delighted

SM

Edited by supermono on Monday 18th December 16:30