saildude:
For a two lane road - get two surface tube type counters - put one sensor in just one lane - put the second sensor across two lanes - subtract the one lane count from the two lane counter to get the count for only the second lane - done all the timebut I do see two tubes for each lane mounted much of the time - I am guessing the counters are used to check each other
two tubes are for speed.
I have seen a black box, about 1/2 inch tall and 10" x 10" that was taped to the road (tar tape) in the center of the lane.
inductive counter, one per lane.
takes about one minute to install
then they just cut the tape and leave the remnants.