Hi Aaron
Nice! I often do this on commuter train rides.
For concentration, meditation words work best for me in noisy environments, when I have trouble tuning into more subtle things like the breath. If I am able to stay still, I often look for an ad-hoc kasina and use that, like a spot on the pavement.
For insight, going for "wide focus" and noticing the impermanence characteristic (beginning, duration, end - any one, or combinations) of those sensations that "want to be noticed" most. If the suffering characteristic works for you, that's great! I wouldn't value some kind of refined existential suffering over good old discomfort, by the way. As I see it, there is just suffering - that's the first noble truth: suffering ist just that; it doesn't come in flavors, it's what's common to any experience of suffering.
Also, noticing the fact that I "lost it" is quite valuable in itself. I note that I got distracted, and am now back on track (I use "back, back"). Something I found useful in addition to noting the return to practice is "backtracking" to when got sidetracked - I do this lightly, because otherwise, I get sidetracked again.

This is great mindfulness training.
I find that practicing in distracing environments is more of an exercise in mindfulness than concentration or insight. Mindfulness is mainly remembering what I'm trying to do, after all.
Cheers,
Florian