River Class Vessel Questions

I am doing research on River Class Vessels and wanted to know the specifics of the class as well as the advantages/disadvantages

Here’s what I understand so far:
[ul]
[li]~650 ft in length
[/li][li]~72 ft beam
[/li][li]15K-20K ton carrying capacity
[/li][/ul]

Here are my questions:
[ul]
[li]What percentage of total cargo does River Class haul on the Great Lakes?
[/li][li]Is this cargo amount growing or shrinking over time?
[/li][li]What is the advantage of River Class vs. other classes?
[/li][li]What ports are used most by River Class?
[/li][/ul]

Any help would be appreciated. Thank you.