Reply #6: It's also an attempt to save the Interstates from truck congestion

[jobycom]

The truck traffic up I-35 is becoming frightening. They are building bypasses around Austin to divert the traffic, but even so, the stretch through Texas is becoming worse. Predictions are that the Interstate will be so clogged in a decade that you won't be able to drive through Texas on the Interstate. This will make travel much more dangerous, and will increase costs and especially pollution as several hundred miles of Interstate highway is clogged with 18 wheelers traveling about 30 MPH the whole way, thus belching smoke for a lot longer. The pollution in central and lower Texas is already becoming critical.

Not saying this is the best way to handle it--I haven't really looked into it much at all. But it does have support from people who are trying to do more than funnel cheap goods from Mexico. As someone pointed out, a railway would be better for that.