Car Impending Collision Detection

Cars should have RF transponders in them that communicate with all other cars near them instantaneously. GPS wouldn't be sufficent to gather each other's immediate positions and velocities, but radio triangulation might. This data can be used to avoid potential collisions: if two cars detect that they're on a collision path, they can together make an avoidance plan and execute it (with automatic steering and/or breaking). This must be last-second (calculated based on speed, traction, weight of car, direction, etc.) because sometimes cars can appear to be on a collision course but it's just due to the shape of a road, traffic lights, etc.

I don't think attenuation-based or pulse-based radio triangulation would work, but maybe phase-based triangulation could?
How to triangulate several cars at once, though?
--they can coordinate to time their output signals to not happen simultaneously
--there can be a whole matrix of tiny antennas and an algorithm sorts it all out.
--each car can operate on a different frequency. the circuitry then either separates the frequencies and then take the phase info (or does it have to use interferometry to get the phases shifts?), or there can be a grid of independent sets of triangulation antennas each working on a different frequency.

or instead of radio, could use ultrasonic location signals? but windspeed must be known?
this could be hell on animals' ears, but perhaps that will keep them away from the roads. not good for pets living very near said roads, though..

Also, a car could have a camera or two (fast FPS) and a computer to in real-time deduce positions and velocities of objects nearby that stand out, then avoid anything that's too big or matches a certain profile (last-second, of course).
this has the following advantages:
-planning collision avoidance can take the environment besides other cars into
account
-it can avoid collisions with other things than just cars.
-it can be used instead of a radio/ultrasonic (relative) positioning system if those are impractical
-it doesn't require other cars to support the same technology.
although it would still help if these cars, independently sensing each others' positions via cameras, could communicate via radio to coordinate their avoidance plans.

perhaps the avoidance algorithm should have some heuristics for dealing with failed tires.

maybe also alternative avoidance branches for people wearing their seatbelt vs. people not wearing their seatbelt. for a person wearing their seatbelt, a head-on collision is better than a collision from their side? and better than a roll? which may not be true of persons without seatbelts on? actually a head-on or rear collision is probably always better now because cars are required to have airbags.