The fair place to meet is El Paso, TX — the city closest to the midpoint of Austin and San Diego. From the farther side that’s about 13 hr 9 min of driving.
Recommended midpoint
El Paso, TX
From Austin
11 hr 4 min
528 mi to El Paso
From San Diego
13 hr 9 min
627 mi to El Paso
Austin has the shorter trip; the split is off by about 2 hr 5 min. The alternatives below can even it out. Austin and San Diego are about 1,155 miles apart.
Austin and San Diego are about 1,155 miles apart by road. Split the difference and you arrive near El Paso, the city closest to the halfway point between them. That puts roughly 11 hr 4 min of driving on the Austin side and 13 hr 9 min on the San Diego side — the fairest single meeting point among the cities near the middle.
Over this distance most people will fly rather than drive the whole way. El Paso still makes a fair, central place for Austin and San Diego to converge, splitting the travel instead of asking one side to cross the country.
If El Paso doesn't have what you're after, Tucson and Albuquerque are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Austin and San Diego.
El Paso is a city in and the county seat of El Paso County, Texas, United States. It is the 22nd-most populous city in the U.S., sixth-most populous city in Texas, and the most populous city in West Texas with a population of 678,815 at the 2020 census. Read more →
Austin is the capital city of the U.S. state of Texas. With a population of 961,855 at the 2020 census, it is the 12th-most populous city in the U.S., fifth-most populous city in Texas, and second-most populous U.S. Read more →
San Diego is a city on the Pacific coast of Southern California, adjacent to the Mexico–United States border. It is the eighth-most populous city in the U.S. Read more →
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.
Estimates use straight-line distance and typical road speeds; real drive times vary with route and traffic.