Rodale built this cool little park across from the Velodrome here. It has three lanes like this:

Walkers l Rollerbladers l Bikes l

The biking lane is the widest. But very frequently walkers will be in the bike lane and sometimes the rollerbladers will be in the bike lane because the walkers are in their lane.

What can I say? People are stupid. Unfortunately I think it's a problem you'll find at all parks and bike paths.