Could we invent a sensor system that detects when motor vehicles are entering a place where no vehicles are allowed, and shuts their engines down?
I think on the Bastille Day massacre. I think of another incident, where a lady plowed into a crowd with her car. I think how such sensor systems might remove or reduce the danger of such things happening. I wonder what the cost would be.
If this would work, if the price is not prohibitive, perhaps we should have such systems at every mass gathering place that could be invaded by vehicles.