The wire loops (in sets of two a few meters apart) are in every stretch of freeway in California. They report the numbers and speed of all vehicles. Have so for decades. This allows the Caltrans operation centers to instantly identify backups due to accidents, etc. Once in a while, the evening news do a story on these operation centers. So we still don't know what the grey sensors do. Note that these sensors are typically mounted only above the two right lanes. --Lucky On Wed, 9 Dec 1998, Michael Motyka wrote:
Lucky Green wrote:
Traffic analysis is performed using wire loops in the the road. The sensors mountend on overpasses near truck scales fulfill a different (so far unknown) purpose.
--Lucky
The wire loops I know about use 60Hz AC and measure inductance. I believe that this would make them unsuitable as speed measurement devices since measurement would extend over a number of cycles. They might work if they were widely separated but you would have to be sure there was only one vehicle generating the peaks.
I'd stick with the speed detector radar for now to explain the overhead doo-dads.
m
-- Lucky Green <shamrock@cypherpunks.to> PGP v5 encrypted email preferred.