Catch drunk drivers with existing technology
There's a fairly nasty failure mode of freeways where some idiot will get liquored up, start driving, and then get on the road going the wrong way. It's only a matter of time after that until something seriously bad happens. When it does, it's usually a huge mess because it's usually a head-on. Two cars meet at 70+ mph each, and ... well, yeah.
Some time back, I had a chat with one of the folks behind the intelligent traffic system in San Antonio. I asked about those induction loops which had been cut into the pavement, and found out that yes, they are a known distance apart so they can figure out speeds from them.
I said, okay, so if this one pulses, then that one pulses, you do the math and say they are going about this fast, and they confirmed that yes, I had the concept down.
So then I said, okay, what if they pulse out of order? That is, the "downstream" one pulses first, and then the "upstream" one pulses afterward? Wouldn't that mean a negative speed relative to normal, or ... a car heading the wrong way? Couldn't you use that to detect wrong-way drivers, shut down a road, and summon police?
The answer I got was less than encouraging. Apparently "it has never happened". Oh, well, great.
Granted, this was about 8 years ago. Maybe things have improved.