Paul_KD7HB:
Multiple tubes for redundancy, not speed. Think of that truck/trailer with 10+ axles with wheels about 8 inches between tires.Paul
Multiple tubes can do both speed as well as vehicle count and vehicle class.
you are correct that a vehicle at 60 MPH with a wheel base of X will trigger the leading tube at a certain delay. a 3 axel with have that first delay, then two rapid ones. a long vehicle will have a long delay, then the rapid ones.
I would expect that by timing and noting the duration between pulses, one could classify quite a bit. the duration between the tube sets the vehicle speed, the time between the first tube's first pulse and subsequent pulses would classify wheelbase.
"Road tubes are used to detect vehicle axles by sensing air pluses that are created by each axle (tire) strike of the tube in the roadway. This air pulse is sensed by the unit and is recorded or processed to create volume, speed, or axle classification data. While one road tube is used to collect volume, two road tubes can be used to collect speed and class data."