The Responsibility of Leading

I was carpooling with Joe Lynch, our alumni guy, to a book event with Gettysburg alums in the DC area last night, but we decided to drop my car in between. He agreed to follow me to the lot and a question occurred to me. Now, I drive slowly (so slowly that I've been flipped off by the Amish), but I realized that the agreement to follow someone to a place you do not know requires a surrendering of autonomy to some degree. Suppose I had decided to speed. He would be lost without me, so he would have to keep pace. If he got pulled over, how much of the responsibility would be mine? Should he expect me to pick up some or all of the fine?