I live about 2 blocks away from a trail here in Minneapolis. In most parts the bike trail, which has only a 10mph speed limit, is separated from the walking trail, but shared trail sections are clearly marked. Also, in most parts the trail is a two-way with a dashed line down the middle, and is a good 3 to 4 feet wide on each side of said line.

Lots of times walkers will use the bike trail for their walking, often walking in pairs/groups that are spread out to take up both lanes and/or not paying attention to the "traffic" acround them. Lots of people like to walk their dogs on the bike trail on long or retractable leashes, so that the dog will run across to the other edge and you are unable to pass them until you can get their attention and they can get their dog next to them.

Unfortunately, if you're not to the point where 25mph is a piece of cake, the streets that run along this trail are more of a problem than the trail itself; lots of drivers speed, ignore stop signs, and other things cops should be around to see.