I believe they're stopped for rain. There was going to be a scheduled break right after the 2nd round of qualifying, but the track decided to try to run as much as the 3rd round of qualifying as possible. The weather radar showed there was a giant green blob heading straight for the track. When I headed home from the track, it was still dry and there was no rain on the drive home but the area the track is in usually gets a lot of the rain in the Chicago area.