At least the Interstate highway takes you somewhere. The Corridor does not connect to any of the major Texas cities.
Hello Lunatic Fringe, guess what! It's not supposed to, hence the name "Trans-Texas Corridor". The idea is to route all of this "trans-Texas" traffic onto a highway system where it is routed around the major cities to help alleviate metropolitan auto traffic and cut down on smog to boot. You might want to read up on it.