Interestingly they couldn't run it during the daytime. Because the roads are open during the day to normal traffic. You can actually see this right now on this streetcam site. If you move the map to Las Vegas, then focus on the Strip (Las Vegas Blvd), and then look at cams around Las Vegas Blvd and Sands/Spring Mountain or LV Blvd and Flamingo, you'll see that normal cars are driving all over.

The streets closed at about 5pm yesterday, and then opened up again at like 5am this morning, which is why there was a rush to get FP2 done, even if during the middle of the night. There would literally be no other time to do it.

Which is interesting. Do other city street races do this? I always assumed the streets were completely closed to normal traffic for the duration of the event. Seems strange that they'd allow regular vehicles on the asphalt. You don't know what random vehicles are doing to the surface. I guess the drivers might like it since they get additional rubbering in? But Idk. Maybe this is normal, and I just didn't know it was happening in Baku, Singapore, Monaco, and anywhere else in other series like Indy. I was in Chicago during the city NASCAR race and I swear the streets were closed the entire race weekend.