[samtho]

Either via RF or line-of-sight IR.

The RF method works the same way ILS for aircraft works: multiple lobes of differing frequencies to a compatible receiver that will only accept the data if both frequencies are present and the interference pattern matches the conditions that it is looking out for.

IR is considerably simpler and would require a receiver to pick up on a well-aimed beam.

For bad actor mitigation, they could put a signature at the end of the speed data that signs the packet with the priority, route, datestamp, and TTL. The priority field could help enforce slower limit around construction zones.