We're about to observe an ingenious device just past the last gates of the last (or first if your transit is Atlantic to Pacific) chambers of the Gatun Locks.

We can only see this when the gate is open. Look just past the gate in the right chamber. You'll see a pair of spans beginning to close across the end of the chamber. These are not gates, but bridge spans. Now look just to the right of the locomotive tracks that go up and above the level of the right gate, you'll just barely make out a white pickup pulling a white trailer waiting there. The same thing is happening on our side too, but the gates hide the bridge that is there just above the water.

Now the bridge is complete and the first vehicle crosses. It's a truck that we couldn't see waiting in the previous picture because something obstructed our view.

Now the second vehicle crosses from the other side. It's either an RV or a bus. The little bump on top is an air conditioning unit.

The white pickup still waits and our container-ship neighbor heads to the Caribbean Sea, as we will shortly.