Also GPS tracking systems are only accurate to about 20m, not enough to avoid hitting stuff. And transmit over the cell network so don't work if you can't get signal.
Although if you're going to be adding to infrastructure, you could just as well add differential GPS transmitters around the place and get the accuracy down to sub-1m[1] although that's still not really safe enough for cars...
[1] (and I believe you can get it down to ~3cm if you have enough data.)
Let's say your car ROMB received info about the white truck, while your car cameras and vision recognition systems see just a cloud and any truck in 100 m range.
ROMB purpose is not to replace cameras or LIDARs, but to extend gathered info.
[1] (and I believe you can get it down to ~3cm if you have enough data.)