This is why connected cars are hoping for a quick spread of 5G. A fully-fledged 5G network would have transmitters placed on every other lamp post with a stable connection to the backbone. With such a system, the rtt should come down to sub-50ms for high priority traffic if properly set up. The obvious downside is the amount of transmitters and fiber you need to set up for this, but the smart vehicle people are seemingly quite confident in their ability to convince operators to install such a network.

A 200ms round-trip would still be comparable to some drivers on the highways right now, but it's certainly suboptimal.