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Sam Wilson · August 2nd 10, 04:45 PM posted to uk.railway,uk.transport.london

In article ,
Jeremy Double wrote:

On 30/07/2010 16:03, Sam Wilson wrote:
In , d
wrote:

On Fri, 30 Jul 2010 07:23:26 +0100
Charles wrote:
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.

In theory , but it would have to be one hell of a small radius curve to
make
a significant difference. Not something you're likely to find on the sort
of roads these cameras are placed on.

No it wouldn't - the difference in distance only depends on the
difference in heading between the start and end points.

The _absolute_ difference in distance (i.e. measured in metres) only
depends on the difference in heading between the start and end points
_and the radial distance between the midpoints of the two lanes in
question_.

However, the relative difference in distance (i.e. the percentage of the
total distance) depends on the total distance travelled. To get a
significant percentage difference in distance (and hence speed), the
change in heading must be done in a short distance, and this implies a
tight curve.

Good point!

Sam