For the past several months I've had my eye on an FKT route, which finishes a few blocks from my house. From a weather standpoint, Sunday was a horrible day to go for it (sunny, typically humid, with highs in the low 90s) but from a scheduling standpoint it was now or wait until next Spring.
A family obligation meant I got a late start: I got back to the house at 7:30 and realized if I rushed to change and pack I could catch the 7:57 train. I supplemented my breakfast with a plain bagel at Union station and made it to the start just after 9am (taking advantage of the porta potties left over from some sort of event the night before).
The first two hours felt great as I was able to chase the lingering shade. I drank a bit over half a liter an hour with Skratch High Carb mix, which went down well. After my first planned Wawa resupply at mile 13, the next few miles were tolerable, but soon the wheels started to fall off. By then it was 90 degrees and full sun and I did a lot of walking to cool off and because my stomach was sloshing.
I stopped again at a gas station in Laurel, right around the halfway mark, for another 2 liters of cold liquids and some ice, which I wore in two water bottles around my waist and stuffed down my sports bra.
As Mike reported this was around the point where the sidewalk ended, so your choice is either the grass or the road shoulder (and sometimes, e.g., when going under 32, the only choice is the road shoulder). This was another factor in my deciding to brave a hot summer day. I thought traffic would be lighter on the weekend and I wasn't sure I'd be visible enough in the dark.
My other resupplies were at a gas station in Waterloo, a 7-eleven between Marble Hill and Elkridge (no bathrooms so do not recommend), and another Wawa just past 695. Each time I bought about two liters of something, with a lot of the water used for cooling/soaking my clothes.
I don't think I digested anything I ate or drank (mostly drank) between hours two and seven, and eventually threw up several liters of liquid (twice). The fact that I felt much better immediately afterwards both times and was peeing normally makes me think that actually I was over-hydrating, chasing the relief of cool beverages. I was sweating much less than usual because I was dumping water on myself every quarter hour or so, which in the case of water on the head felt like it evaporated instantly. After the second emission, somewhere around Elkridge, the slightly cooler temperatures and fact that I'd learned my lesson about not pushing fluids meant I was able to run it in from there fairly comfortably. At the final Wawa I gave up on electrolytes and bought a 500ml coke, which I finished a few miles before the end.
Aside from the heat and stomach issues, everything felt fine, and weirdly for how bad my fueling went, I neither bonked nor felt dehydrated.
There is lots of traffic on this route and you're pretty close to it for 15 miles or even more. I got a lot of friendly honks from drivers and never felt unsafe, but I think the Sunday holiday weekend may have contributed to the chill vibes. This is definitely something to be careful about if anyone attempts to route in either direction.
All that said, I found it really empowering to run all the way back home from DC. It turns out it's not that far! Though I found it a little depressing that the major highlights tended to be familiar highway crossings, though I did also notice the UMD campus (a nice surprise), the Patuxent River, and the Patapsco River (my favorite). The first 13 miles out of DC are really quite nice and could include very minor detours on some nice looking trails and bike paths. So if DC folks want to run a half marathon essentially all on Rhode Island avenue to Maryland and back with a resupply at the Wawa that could be nice, with some rolling hills to keep things interesting.