I have regularly taken two-day trips in the US because the cost of an airplane for 5 is much more than the cost of my car even including hotel rooms. Lately I've been taking Amtrak, which is a little bit cheaper, but it's still annoying enough that I would only do it because I hate driving.

It also helps the economics to realize that there are very few places in the US that anyone would go that not having a personal car is a reasonable thing and so you have to have the cost of a rental car to anything other than grabbing your own.