Yeah, there were some fun specs on those projects. The one I had to deal with was in vehicle separation. We needed to determine when a vehicle entered the toll zone, and when it left it, to within a few milliseconds. Needed to work on motorcycles, cars, trucks, and correctly identify trailers as part of the same vehicle! Of course, when I got to the actual installation, I saw that this was in the car pool lanes of the highway, so it was illegal to tow a trailer there! But, it was 'in the spec!'
Solved that one by using multiple laser sensors, and combining them in a logic box to identify when a valid signal was detected. Should'a patented that one, but the company wasn't into getting patents on its technology. They were probably infringing on too many already... 8-)
My favorite part about the antennas was that they were mounted by a pair of U-bolts. Worked great, until the wind came up. Those almost meter square antennas had a lot of sail area, and unless you REALLY torqued them down, they would slowly rotate!
Charlie