The Rail Accident Investigation Branch (RAIB) said the broken sections were part of an auger drill that had "penetrated the tunnel lining before falling on to the track".
Brickyard Crossing, which used to host a Senior PGA event, is truly one-of-a-kind: four holes play inside the infield of the oval track, often with loud cars running by on test laps, linked by a tunnel to the fourteen holes just outside the stadium.