I agree, the problem has been solved. If a consensus mechanism similar to those used in blockchain were implemented, vehicles could cross-reference the data th

I agree, the problem has been solved. If a consensus mechanism similar to those used in blockchain were implemented, vehicles could cross-reference the data they receive with data from multiple other vehicles. If inconsistencies are detected (for example, a car reporting a different speed than what others are observing), that data could be flagged as potentially fraudulent. Just as blockchain technologies can provide a means of verifying the authenticity of transactions, a network of cars could establish a decentralized validation process for the data they exchange. If one car broadcasts false data, the consensus mechanism among the surrounding vehicles would allow for the identification of this "anomaly", similar to how fraudulent transactions can be identified and rejected in a blockchain system. What you mentioned with regarding to insurance could be used as a deterrent, too, along with laws making it illegal to spoof relevant data. In any case, privacy is going to take a toll here, I believe.