Going home should not have been difficult and if I were a more organized person it wouldn't have been. The thing is the Air and Space Museum is closer to the L'Enfant Plaza Metro Station than it is the Smithsonian station, so I aimed for L'Enfant Plaza, where I managed to get lost and wander around block after block of 1970s-style concrete patios following signs that hinted at the existence of a Metro station without ever promising that one would, in that or any direction, actually find one. I'm here, now, so I got back somehow, and that somehow was by giving up, returning to the National Mall, and walking to the Smithsonian station. I greatly appreciated that I'd arranged to have the hotel's shuttle service pick me up rather than tromp on foot the way back.
For driving back I realized that any plans I might have had to be there by early evening were hopelessly wrecked; it was already around 7 pm and while my parents might make that drive in about three hours I clearly lack whatever moral virtue it is that allows people to make long drives efficiently. I decided to get something real to eat on the road, at some Interstate rest stop somewhere, and not to worry about it otherwise.
I had a few surprises driving back even compared to the drive down --- where the big surprises were first that Delaware was closed (or at least both its Interstate rest stops on I-95 are closed, which is surely equivalent) and that the toll for a Baltimore tunnel was a shockingly low $2 rather than the eight or ten bucks I expected from experience with New York City area tunnels. In particular there wasn't a toll going the other way, although one-way tolls aren't unknown in the New York City area either. Also construction which was faintly irritating Thursday night was inexplicably absent Saturday night.
I stopped somewhere in Maryland for food, which turned out to be a Sbarro pizza and slice of cheesecake, eaten late enough that they were closing off sections of the seating and wiping down seats with the same cloth used to wipe off the tables, a practice that I will pretend I don't see at least as hard as I'll pretend it's sanitary.
As the hours wore on I finally crossed into New Jersey and stopped at the John Fenwick service plaza, named for a person even his own family doesn't know anything about. Also I got started to fret about whether I should fill up the gas tank: I had something like a third of the tank left, by the gauge, but as with all cars for some reason that last third goes a lot faster than the first third does. Yes, gas stations are not rare things, but gas stations on the Turnpike and I-195, which would be most of my remaining ride, are increasingly rare things. I knew that when the low fuel gauge light went on I'd have about thirty miles or so to do something, which should be enough to get to a gas station ... if it weren't getting awfully close to midnight on a Saturday when the open gas stations start dwindling to select Wawa stations. But then I was awfully close to home already; I might easily make the sixty or so miles I expected left before I got to the low gas light. But ... if I ran out it would be a nuisance. Not so much of one as there's rescue squads patrolling the Turnpike and 195 who'll give a couple gallons to the stranded motorist, but waiting for them on top of that ... but it would be awfully cool to make the trip down and back on a single tank of gas. But it would come in about 400 miles total, while I've never got more than about 360 miles on a single tank. But that was with a lot of local driving, while highway driving is significantly more efficient, and I did have more than a quarter-tank left by the gauge. But ...
Well: the lines at the Fenwick service plaza for gas were way too long to wait for. So I continued driving and trusted I couldn't run out before whatever the next plaza was. And I didn't, at that; I pulled in to the next plaza with more than a quarter tank and felt a little silly bothering. When I did get home I found that the round trip was very nearly exactly 400 miles, and that I was getting just about 35 miles per gallon, so that I'd certainly have been able to make it round-trip without filling up. Good to know for the future, if I were to make the trip again, I think.
Trivia: On 6 July 1864 Napoleon III ruled that while the Egyptian government could end the corvée --- forced labor --- used for canal-building, it would have to pay the Suez Canal company 38 million francs in compensation. Source: Parting the Desert: The Creation of the Suez Canal, Zachary Karabell.