I don't think adding RF emitters / magnets to the road surface actually solves any problems. A driver needs to know the trajectory of the road several seconds into the future. At useful speeds, that's on the order of 100 meters. Either you dynamically generate a map in a local reference frame, or you localize within a static map in a global reference frame. RF beacons won't provide enough resolution to be useful for dynamic mapping beyond a couple of meters. RF beacons may incrementally help with localization within a global map by providing additional observations for a localization filter, but no one doing global mapping is asking for that since they're already using lidar to do it.

I think useful "smart" road infrastructure would necessarily be horribly complicated, since the point of it would be to offload otherwise necessary complexity from the vehicles using the road. Perhaps the road could track the real time kinematics of all the cars on the the road using some combination of cameras, lidar, UWB, etc. It could then communicate that information via RF to the vehicles that want to receive it, along with local mapping information.

The automotive industry has been excited about "vehicle-to-vehicle" comms for the past 15 years aka V2V. Technically, all the standards that have emerged from the industry's efforts seem lame and nothing interesting has come of it. The FCC granted a chunk of 5Ghz spectrum for automotive DSRC use, and have subsequently taken back most of it for lack of use. It's still allocated for automotive, but it's now in the hands of the cell modem providers to do something useful with it.

How does one power active RF emitters on miles and miles of road surface? The vast majority of surface level roadway doesn’t even have powered illumination in most places, which leads me to think the lowest hanging fruit for this type of thing would be something passive, like the RF equivalent of cats eyes.