How can we measure the volume of vehicles in a traffic flow?

Question

Is there a unit (e.g. number of vehicles per second?) that is being used to measure the volume of traffic flow? What is it?

Answer 1

It's usually vehicles per hour.  Number per second would be a bit small for some streets.

Answer 2

I have seen a little rubber hose thing that goes across the street between center and one side ... I assume they using this to measure rate of # sets of wheels passing there at a particular time of day.

I also note that some left turn lights don not kick in when no one needs to turn left, so whatever mechanism used there, and at traffic lights in general, may be useable to measure # vehicles by lane, to give more heavily traveled direction proportionally more time to get through.

There's digital cameras being used for security purposes.  I imagine that footage could also be used to count vehicles in some time frame.