Earlier quoted context omitted.
about a 350 mile trip, 20 miles per gallon That would be 17.5 gallons each way, not 30. The round trip is then 35 gallons, which should easily be less than three 15-gallon tanks. Even 450 miles each way fits in three tanks. Only for short trips does driving beat the cost of flying I don't know how much you can stick to highways on that DC-Boston route, but when I drive down to visit my parents, each way is 400 miles…
In my case, I need to refill my 15 gallon tank 3 times for the whole roundtrip. So, my best case is 45 gallons, which at $4/gal is $180. It's true I'm left with some gas at the end, so perhaps that skews the calculation. If I could refill it with just enough, I could shave some bucks. But I prefer not to return home on empty fumes. Next time you do the trip - calculate the cost. You'll see it's closer to the best air…
You've ignored the costs (both monetary and opportunity) of renting a vehicle or using public transit while in the destination city as opposed to having your own vehicle there. You've also ignored the potential harm of being confined to a cabin with scores of people who might be carrying airborne pathogens. You haven't considered the emotional cost of being subjected to an invasive search at the airport, or the stress of getting to your gate on-time.
To be clear, I am not anti-flying. I just think it's a sad state of affairs when it's more economically rational for a single individual to drive 450 miles each way than it is to fly. Get a more efficient car, add another person or two, require some bags, or plan an extended stay, and anywhere within a 12-to-24-hour driving radius becomes an economically irrational flight.