I’m probably underestimating this by a lot, but is it that much work to change it? The infield course is already there, so isn’t it just moving barriers to turn 1 and painting a couple more lines?
Yes, you're underestimating it ... by a lot.
When SVRA first went to Indy to put on the Brickyard Vintage Racing Invitational, I was lucky enough to work it. In that first year, they offered to the drivers not just the road course for the usual races, but exhibition laps on the oval at racing speed. Needless to say, it was a huge selling point.
However, the time it took to convert the track was tremendous. The oval requires a certain setup of walls, especially on the inside of turns 1 and 2, which cannot be there for the road course. Mainly due to the angles the drivers would otherwise inpact inside barriers if they spun to the inside of the oval. They also have to add barriers in Turn 4 when they run the road course in order to protect emergency vehicles which sit there for rapid deployment for the early part of the infield circuit. They also have to add walls in the short chute between 1 and 2 for the cars exiting the infield, again all due to angles. And if I remember correctly, the entrance to pit lane when running the road course is different than the exit of pit lane when running the oval, requiring more wall movement.
So, they only wanted to do this conversion once a day. Thus, they would setup for the oval at the end of one day after racing was complete, run the oval the next morning, and then change it back during a long lunch.
After two years of this format, they abandoned the idea of providing racing speed laps on the oval. It was just too much of a hassle. (Occasionally they did have some ceremonial runs on the oval, but they were very slow speed, so they just shoved the walls that were placed on the oval out of the way.)
And yes, I did get to drive the oval -- in a Jaguar F-Type. It was one of the most overwhelming experiences of my life.
