High up scamera van

[Prof Beard]

A week or two back I was driving out of Stoke-on-Trent and noticed - a couple of hundred yards AFTER a single file 30mph coned section - where the road had opened up to two (both) clear lanes again but BEFORE the 30mph ended - a scamera van parked high up on a flyover crossing the road in such a postion as to monitor the traffic below.

Question: what effect does using a fairly scharp downwards angle have on the accuracy of the equipment used?

Prof Beard

[timtonal]

Prof Beard said:

A week or two back I was driving out of Stoke-on-Trent and noticed - a couple of hundred yards AFTER a single file 30mph coned section - where the road had opened up to two (both) clear lanes again but BEFORE the 30mph ended - a scamera van parked high up on a flyover crossing the road in such a postion as to monitor the traffic below. Question: what effect does using a fairly scharp downwards angle have on the accuracy of the equipment used? Prof Beard

Cosine effect makes device read less than actual speed travelled....
www.speed-trap.co.uk/Accused_Home/How_it_Works/How_it_works_Home.htm

Website said:

Cosine Factor You remember cosines don't you? Sines, cosines and tangents - all that mathematical guff at school that made you nod off into a nice, deep slumber at the back of the class. Well pay attention Double-0-7! Radar only works to detect the true speed of a vehicle if the radar is in the vehicle's path If the radar is positioned at an angle to the path of the vehicle, as in a GATSO camera, the apparent speed of the vehicle is reduced. The reduction in speed is proportional to the cosine of that angle. For example, at an angle of 15 degrees, a vehicle travelling at 40mph would only be measured at 38.6mph. Seriously. Look - cos(15) = 0.966. So 40mph x 0.966 = 38.6mph. GATSO cameras and other roadside devices have circuitry designed to compensate for cosine factor. The units must be aligned correctly according to the manufacturers instructions in order for the circuitry to do it's job correctly. In short: Cosine factor is always in favour of the driver.