Wellllll: I have proven myself not to be a prophet. When Texas got started on their planning and after me being a few years in California, I was of the opinion that Texas would be up and running before California got through talking. While the most significant parts of California are yet to be, at least the middle (and easiest to build) segment is well under way.
This "build in the median of an Interstate" is a bad idea that will simply not go away. Three primary reasons: Inadequate vertical clearance under overpasses, meaning ALL will have to be rebuilt. Likelihood of the median being inadequate in width throughout, Interstate design speed is 70 mph, although many states will use higher speeds, terrain permitting, this means curves will not likely permit 180 to 200 mph speeds. (Allowable speed on curves is proportional to V^2, not V, so if you double the speed, the minimum radius must be increased by a faactor of 4., or if triple, by 9.) "Build in the median" works for urban transit because the speeds are low, and normally vertical clearance is sufficient. However, in many cases there is no usable median width in urban areas as there is no space between the opposing directions of traffic beyond that needed for a barrier wall.
If it is decided to go to making improvements to an existing line, there are two possibilities, both routes that had passenger service in the past, and neither would be cheap to upgrade. The less likely would be the UP, ex SP route that goes through Bryan / College Station. However, it was the slower of the two and currently has considerably more freight traffic, so as well as working with a less cooperative railroad it would cost considerably more to achieve reliable 90 to110 mph passenger service. The other, although with no significant intermediate points other than Corsicana, would be the BNSF ex Burlington Rock Island line. The freight traffic level is fairly low and BNSF has a good alternative in the ex AT&SF line. This line had 4 hour service at least into the early 1960's. However, it probably has a gazillion road crossings, many likely having low road traffic, but used by drivers anticipating low frequency 40 mph or slower freight trains. The track is probably in barely there condition. Looking at old accident reports, there was a derailment in the late 1940's that described the line as being unsignaled and having 90 lb/yd rail. It did get ABS after the less than 80 mph with or less than 60 mph without signals rule came into effect, but the ride quality in the last several years of passenger service was best described as exciting. Saying this to say that the line would probably require subgrade up track improvement throughout.
