This also assumes the radars are using as much bandwidth as Wi-Fi, and that the noise floor is the same, and that Wi-Fi-like modulation works fine for radar, etc.
Keep in mind this was an OOM argument. How much info does one really need to collect from the radar? 1-10kb/s?
Even with 10 cars trying to scan the same region, that's about 5 OOM of headroom compared to wifi.
Also consider what modern military radiation radarss can do. The F-35 can actively track 50 targets, all in one direction. And it can do that while potentially 100s of aircraft all are sending radar beams into the same space, with some even activelly trying to jam the F-35 radar.
Obviously, really old and cheap radars can have interference issues. But any such limitation is not due to the Physics or even engineering, but rather on the cost of a radar sophisticated enough to handle its environment.
