How do the overhead sensors work that are on freeways (in CA) near public scales. Are they magnetic or what?

Question

There are perpendicular modules on poles that hang over the traffic lanes as you get near the scales and then a large parallel one right alongside the scales in the right traffic lane. What/how are they sensing? They seem to be sensing loads or vehicle weight, but they are overhead. What technology do they use?

Answer 1

those things over hed you speak of are for a nation wide system call Prepass it is for trucks ( 18 wheelers) there are sensors in the road that weight the truck and in the cab there is a little black box that tells the driver weather or not to pull in to a weight station it is like the same thing you can get for a toll road so you dont have to go to the booth and the dont sense the load just for weight and the companys safty record if you are over loaded the little box has a red light on it and a voice will tell you to pull in to the scale
hope that anwsers your question