I don’t think it was originally designed as anything other than a sidewalk, certainly not a mixed-use trail. The southern portion, around the Pentagon used to be a sidewalk, too. What’s there now, is a result of the post-9//11 rebuilding.
I’ve never had a problem passing runners and non-tourists, but I use a bell and then call out. (Every now and then, I’ve encountered some tourists who just stand there and look at me, without moving.)
The worst part of the “trail” is the portion just before and after it crosses over Rt 110. Without widening the bridge, there is not an easy solution, since ground drops quickly away on both sides, but it need the most work.
Taking the trail in the direction he takes it, south, I don’t find those ramps to be a big problem. (The heaviest traffic is the one at Memorial Bridge.) As he mentioned, they are all worse, traveling the other direction, when you have to look back to see traffic. While I do not dismount at the ramp crossings, if you stop and dismount, you can get a clear, unhurried view of each crossing and walking (or running) across does not take much longer than riding (if you stopped). If you only want to slow down and not actually stop, much less dismount, then they are a problem. Could the actuall crossings be better? Yes, but I don’t think they were designed with cyclists in mind.
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