Is it really that difficult to have the vehicle's on-board computer measure stopping power and vehicle weight, and transmit those calculations to the lead vehicle's computer? If each car's variables are included in the initial contact, the lead vehicle's computer could determine whether or not that car is allowed to join based on the current speed being traveled by the road train.Based on the variables, each car would need to maintain different "optimal" distances from the car ahead. Far enough for safety, but close enough for efficiency. If your car requires too much distance from the car ahead that it would ruin the slip stream, your car would be refused permission to join. If you really want to partake in these, and you're refused often enough, you'll get off your ass and get your car fixed.