It's only cheaper because you're ignoring wear and tear (aka maintenance), depreciation and insurance in your calculation. Not to mention it's incredibly unsafe to do a 26h ride in two days instead of three - you don't want to do a 13h ride, so realistically you're looking at two days of some motel to stay over night.
For what it's worth a proper high speed train could do a 10 hour run at 300-350 km/h. Not exactly the ~900 km/h of your typical airplane, but at least you 'll have a decent seat over the travel time.
A 10-13h drive (with breaks) on a modern (say > 2009) car is surprisingly non-strenuous on US interstates. I've done it and it was not onerous. The driving experience in the U.S. is markedly different from other countries -- interstates are wide and relatively smooth-flowing outside major cities, and rest stops are plentiful.
To most Europeans a >10h drive sounds excessive, and that might be the case in certain parts of Europe, but the U.S. is (perhaps unfortunately, from an environmental perspective) built around the automobile, and the driving experience here is somehow different (i.e. easier).
I've driven in Germany and while I enjoyed spending hours cruising on the Autobahn (A-8), parts of the journey involved driving on tiny, narrow roads in small towns. Those segments were frustrating. I haven't yet tried it, but I don't think I'd be able to drive > 5 hours in Europe (but I could be wrong).
I find the more frustrating part of driving on the Autobahn being the constant changes in speed limit. You cant just cruise 170kmh all the way, since theres so many construction along the way plus the random 90kmh zone here and there.
Phoenix to Chicago is about 1700 miles. At 70mph moving average it's a 25 hour drive. Trucking regulations allow a 14 hour drive, ten hours rest followed by I believe a 12 hour drive. It might be strenous but it's not dangerous.
Also keep in mind 1700 miles at the IRS standard deduction of 55 cents a mile is $935. Assuming your car seats four (and all four seats are in use) that breaks down to just under $200/person.
Whoa, WTF? In Europe, it's 8 hours regularly with 2x a week allowance of 10 hours (to be used e.g. in case of massive traffic jams), followed by at least 11 hours.
Why is there some physiological reason that makes longer drives unsafe? In my experience I can drive as long as I can stay awake, which I can certainly do for 13 hours in a stretch (and then some). I find it easier to be the driver than a passenger, for that matter, as at least I have something to do.
Even if you can manage to stay alert for so long, wide parts of the population cannot, which is why maximum limits have been introduced for commercial drivers everywhere (and accidents rates have fallen correspondingly), and why in accidents drivers who have been on the road too long are generally found to be at least partially at fault.
Additionally, who says you're actually able to drive safely after 13 hours and react to something like, let's say, a child hopping in front of your car and that you just have been extremely lucky?
For what it's worth a proper high speed train could do a 10 hour run at 300-350 km/h. Not exactly the ~900 km/h of your typical airplane, but at least you 'll have a decent seat over the travel time.