I recently bought an antique Mack tractor trailer, and in order to be able to drive it, I went to truck driving school. I now have a California Class A commercial license, and can drive just about anything except hazardous materials and tankers.
One of the main things about driving a tractor-trailer is knowing where your trailer is, and making turns so it doesn't crunch the stop sign and bicyclists along the way. A long trailer is tricky to manage, and you have to swing wide on the turns, as I'm sure you've seen drivers do. And backing up a long trailer is no small thing.
Yesterday a "hook and ladder" fire truck turn left in front of me and I watched the guy in the very back skillfully driving the back end of the engine around the turn. This is not so easy to do, as you might imagine. But I found myself thinking about the guy driving in the front of the truck.
I can drive a truck with a 50-foot trailer, but the game changes, it seems to me, when there's another driver swinging the back end around. Much of it is good, since you don't have to take the turns so wide, but it also seems just downright weird, to take a corner with a 50-foot trailer and not have to worry about the back end of it! They call these "tiller trucks".
There must be an amazing amount of communication and trust between these two drivers. I can't think of anything else that has two active drivers piloting the vehicle together as a team. Co-pilots of airplanes take turns, for example; it's not as though one of them flies the back end of the plane while the other flies the front.
Just another reason to admire fire fighters, I guess!