I've made this suggestion before, but all commenters remarked about the risks of trusting another car, trusting another signal, hackers, script kiddies, and other malicious agents. The safest inter-car communication was determined to be adaptive cruise control.
Look at it this way; if you get false positives about hazards in front of you, the consequence is maybe you slow down unnecessarily. If you get a false negative, that's really no different from no data at all - your car should behave the same.
https://storage.googleapis.com/sdc-prod/v1/safety-report/way...
I'd expect the opposite - a self-driving car might outperform human drivers significantly in conditions where we tend to underperform - poor visibility, longer braking distances, poor steering control - because it will be more effective at adjusting than a human.
This is the wrong way to think about it. An autonomous transportation service that works only in great weather is already a multibillion dollar opportunity. The revenue from providing services in places like California and Arizona can fund expansion into harder areas.
Nobody said that PCs were useless in the 1980s because many parts of the world didn't have reliable electricity. Nobody said web search was useless in the 1990s because most of the world didn't have Internet access. Likewise, you don't have to solve for driving in monsoon rains or Indian traffic before you can print money with autonomous vehicles.