If they had ultra-wideband transceivers on each vehicle, wouldn’t that let them determine direction and location down to maybe (i’m guessing) 10 cm?

If all cars could detect these kinds of beacons, i’d want a transmitter on my bicycle. Or, carry one (my iPhone?) as a pedestrian.

DSRC and cellular-V2V i think solve similar problems, but those two require the more inaccurate GPS, i think,.