This can fail horribly. Consider that the truck can decelerate faster than its solo braking ability by hitting a wall or another car. Chain reaction pile-ups

This can fail horribly. Consider that the truck can decelerate faster than its solo braking ability by hitting a wall or another car. Chain reaction pile-ups aren't only about reaction time. So, you can count on not being forced to collide by the driver acting alone, but it takes some extra margin to reduce the threat of rear-ending by a poor braker following you, and to account for obstacle-assisted braking by the driver in front.