On 30/07/2010 07:23, Charles Ellson wrote:
On Thu, 29 Jul 2010 14:28:53 -0700 (PDT),
"jonporter1052@btint ernet.com wrote:

On 29 July, 15:15, wrote:
On Thu, 29 Jul 2010 15:01:56 +0100


Paul wrote:
In , David Walters
writes

On Thu, 29 Jul 2010 14:08:34 +0100, Paul Terry wrote:

Added to which, it has been widely reported (and confirmed by the
cameras' manufacturer) that drivers can defeat a SPECS camera by the
potentially unsafe practice of lane-hopping during the measured section
of road.

That hasn't been the case since sometime in 2007.

http://www.theregister.co.uk/2008/07...d_camera_myth/

Ah, glad to hear that that loophole has been closed.

Did anyone believe it worked anyway? Why would anyone writing the software
make the cars lane part of the database key in the first place? It makes
no sense whatsoever.

Possibly for the sake of simplicity to allow for e.g. the difference
in speed between two vehicles remaining in parallel in lanes 1 and 4
where there is a significant curve between measurement points. If the
usual 10% etc. tolerance is ignored and speed limits applied strictly
then in theory it would be possible for the two vehicles to stay
together with one under and one over the speed limit.

Do the maths... the standard lane width on a motorway is 3.65 m, so the
maximum extra distance, even assuming the motorway does a 90 degree
turn, is 3 * PI/2 * 3.65 or about 18 metres. Assuming the average speed
cameras are fairly close, say 1/2 mile (or 800 m), this is only 2% of
the distance (and hence a difference in speed of 2%).

In practice, there aren't many (any?) motorways that do a 90 degree
curve in 800 metres, so the difference in speed would in practice be
less than this.
--
Jeremy Double {real address, include nospam}
Rail and transport photos at
http://www.flickr.com/photos/jmdoubl...7603834894248/