Merging Traffic

This is off-topic, but I like ships too -- who doesn't? -- so....

We were gone for a short vacation in the St. Louis area.  No railfanning, I'm afraid, but we spent some time sitting on the dock at a bar in Grafton having a few beers and watching the birds and the boats go by.  Who could ask for anything more?  Grafton is where the Illinois flows into the Mississippi, and there's lots of barge traffic on both rivers.  And while we were there, in the foreground is a tug coming down the Illinois, pushing a long string of barges at full speed.  Behind it in the distance you can see a similar string of barges coming down the Mississippi; the tug had slowed down as much as it could to yield the right-of-way.

In the absence of block signals (and emergency brakes!), they must obviously have a well worked-out system to avoid collisions.  It was certainly interesting to watch.