A better solution would be to provision each car with its own key pair and the car maker's root CA just before it rolls off the factory floor, that way it can constantly beam 2 signals:

- a signed (regulator-mandated) signal for cars from other manufacturers;

- an encrypted signal intended for cars from the same manufacturer.

The first signal would be signed by the root CA of the car maker to indicate that its communications can be trusted.

The encrypted signal would of course carry an information-rich payload for coordinating a convoy to travel at the same speed, brake, signal a turn, etc simultaneously, for instance.