^ Are people going out of their way to avoid I-10 between San Antonio and El Paso? Because the traffic volumes bottom out to around 4,000 AADT.
San Antonio to El Paso is the longest stretch of I-10 without any significant destinations in between. Very little cross-country commercial vehicle traffic will stay on I-10 for its entire length thru Texas, due in part to some of the really odd jogs the route takes crossing Texas. I-10 takes a hard turn at Las Cruces and another hard turn at San Antonio. When you look at the US map it's easy to see Las Cruces is literally due West of Abilene. I-10 was still completed (for the most part) anyway for the sake of consistency, safety and having a logically complete
national system. The Interstate system is not supposed to be a hodge-podge of different highway types.
I-10 doesn't have the same safety hazards as US-290 near Fredericksburg. I-10 is at least a divided and
mostly limited access route. There are more services along the route, more lights, more activity, etc. Driving on desolate roads in West Texas can be a scary experience, particularly at night. I've driven on US-82 at night between Lubbock and Wichita Falls during the fall when deer are in the rut. That can be a white knuckle experience there. US-290 out near the I-10 junction looks like it could be every bit as hairy.
The low AADT counts on both I-10 and US-290 can
and probably will change, due in part to the business and distribution center growth in the Austin area. Amazon, Google, Tesla, etc are building big there. Bypasses with freeway upgrade potential are going to be urgently needed for Johnson City and Fredericksburg. TX DOT at least needs to get US-290 turned into a 4-lane divided highway to the US-281 corridor just to preserve ROW for the future. On top of that TX DOT needs to be looking at TX-46 between Boerne, Spring Branch and New Braunfels.
I get it that freeway (or toll road) upgrades are very costly. OTOH, the section of US-290 between I-10 and Johnson City would not be all that bad. The super highway upgrades come at a cost of that region having the fastest population growth in the nation. The San Antonio and Austin region together is 5 million. And that's going to keep growing.