Houston to Dallas via Amtrak is possible. It's also about 20 hours and $70. And leaves once a day. Sure, you say, that's because there's no direct route. True.

Houston to Dallas via Amtrak is possible. It's also about 20 hours and $70. And leaves once a day. Sure, you say, that's because there's no direct route. True. San Antonio's better: 5 hours and $34. Still leaves once a day. At 7pm.