I have always understood why Austin was bypassed in the original interstate proposal. That has never been argued. San Antonio was way bigger, plus a base city and Austin was like Waco is today. I grew up here and even in my short lifetime it was at one point still a sleepy little town. I have never argued why a Houston-Austin interstate wasn't built in the 1956 plan. I have said, now that its not 1956, why are we still operating like Austin is still at 200,000?
Also, when the system was laid out, Albuquerque was about the size of Austin, yet got I-25 and I-40, so sometimes lack of population is a week argument.
In that instance, that just has to do with the previous routes both interstates were following. They just happen to junction there.
I-27 between Amarillo and Lubbock was authorized in the 1968 additions and constructed until the 1990s. The entire route was already a four-lane divided highway, the project required frontage roads, overpasses, and ramps constructed along most of its length, and a few new terrain segments.
What warranted an interstate to connect two cities of 200,000 and 250,000 (today's population, likely lower in 1968), but the state capital and Houston, both of which have a population of over 1 million each, still lack a connection today?
To give you an idea, I-27 has lower traffic volumes in many locations than US-290 or SH-71 do between Austin and Houston.
I'm not against having I-27, but I think that a connection between Austin and Houston, or along the US-59 corridor north or south of Houston, would've been a higher priority. But it's likely that there was political motive in getting I-27 authorized and funded.
Now I read that, and I think every interstate ever built faced those same things. Either cutting off access or the building of frontage roads. There are over 3,000 miles of interstates in Texas built with long frontage roads. What makes this project so special that you can't build frontage roads in this particular situation? If that was such a hurdle, none of the interstates would have been built.
That argument does seem surprising in my mind, especially considering TxDOT has over 80 miles of frontage road projects planned to complete I-69E and I-69C in southern Texas over the next decade, plus the I-69 upgrades leaving north and south of Houston along US-59 which are constructing miles of frontage roads.
I personally don't like the expressway model because it's so unsafe. Who wants to drive 75 miles per hour with driveways entering the main lanes? Stuff like that is what kills people. Make it an interstate for the interest of safety.
I've usually never had any issues with drivers impeding traffic flow by entering. The volumes are low enough that there's gaps in traffic from time to time that allows a safe entry. The risk does still exist though, and an interstate highway would reduce this significantly.
75 mph is an appropriate speed limit for the expressway model and represents the speed most people drive.