Houston to Austin seems to take 50 minutes by flight vs. 2 hours and 30 minutes by car. That's not the best convenience ratio for a domestic flight (going between the two largest cities in Denmark is 40 minutes by air vs. over 3 hours by car), and it's certainly more expensive...

However, whether it's more polluting actually depends on a lot of things. Comparing a fully booked, modern commercial passenger plane vs. a car carrying a single person usually has the airplane coming out on top (heh). A modern car with all seats occupied beats the airplane though.

(A naturally aspirated V8 without direct fuel injection leads to a divide by zero in any efficiency calculations.)