Radar is very useful but doesn't replace a lidar. Radars give very accurate readings of an objects distance and relative velocity but very poor angular resolut

Radar is very useful but doesn't replace a lidar. Radars give very accurate readings of an objects distance and relative velocity but very poor angular resolution. For that reason they aren't much use for avoiding stationary objects since those are hard to distinguish from the ground, signposts, etc. At least until they get so close that the radar field of view lets you rule out those things. They are really great at figuring out whether cars are braking, though, since cars are moving with respect to the ground you can just filter the ground out and with radar you can sense the change in speed directly rather than having to figure out the speed by comparing distance over time. EDIT: Actually, I think automotive radars don't give any directional information at all since they don't use big dishes. I'm used to working with aerospace radars but even with those I wouldn't rely on one for car navigation.