The fair place to meet is Oklahoma City, OK — the city closest to the midpoint of San Diego and Washington. From the farther side that’s about 24 hr 6 min of driving.
Recommended midpoint
Oklahoma City, OK
From San Diego
23 hr 52 min
1,138 mi to Oklahoma City
From Washington
24 hr 6 min
1,149 mi to Oklahoma City
That’s an even split — both sides drive within 14 min of each other. San Diego and Washington are about 2,270 miles apart.
San Diego and Washington are about 2,270 miles apart by road. Split the difference and you arrive near Oklahoma City, the city closest to the halfway point between them. That splits the trip almost evenly — about 23 hr 52 min from San Diego and 24 hr 6 min from Washington.
Over this distance most people will fly rather than drive the whole way. Oklahoma City still makes a fair, central place for San Diego and Washington to converge, splitting the travel instead of asking one side to cross the country.
If Oklahoma City doesn't have what you're after, Dallas and Kansas City are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between San Diego and Washington.
Oklahoma City, often shortened to OKC, is the capital and most populous city in the U.S. state of Oklahoma. It is the 21st-most populous U.S. city and 8th largest in the Southern United States, with a population of 681,054 at the 2020 census. 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 →
Washington, D.C., officially the District of Columbia and commonly known as simply Washington or D.C., is the capital city and federal district of the United States. 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.