OK this band is reserved so there should be no direct interference with other devices, but what about interference with the radar on other cars? In heavy traffic there could be dozens of competing radars bouncing around.
Also interference isn't just a matter of the same wavelength. When these radars are common there will be lots of energy in this band, in continually changing patterns as the transmitters move. That is going to produce some very weird effects on other devices even if they are not tuned to that particular waveband.