The NASCAR Cup Series has explained how an ambulance was able to drive down pitlane entry as the field pitted under caution during last weekend's regular season finale at Richmond.
Danica Patrick's spin on lap 256 of the 400-lap race triggered a caution that prompted a number of drivers to pit while an ambulance was entering the pits.
Polesitter Matt Kenseth damaged his Joe Gibbs Racing Toyota's radiator after hitting Clint Bowyer as those pitting slowed to avoid the ambulance.
Other drivers swerved onto the track before crossing back over the pitlane line, with NASCAR waving all commitment line violations during the incident.
NASCAR senior vice president of competition Scott Miller explained that the ambulance driver had ignored a race tower instruction.
"We had a situation where a directive was given from the tower and it wasn't followed," said Miller.
"We'll do our due diligence to figure out why the directive wasn't followed and make sure we're prepared never to make that mistake again."
Miller admitted closing pit road could have prevented the incident.
"We probably should [have closed pit road]. Those calls are very dynamic in that they happen very, very quickly," he added.
"It's the race director in charge of pit road open and close and the track services and safety crew in charge of the other.
"We didn't sync up tonight. We will make sure that we don't let that happen again.
"It's very tight at pit-in and as I said, we will analyse the situation and do a better job."
Kenseth said he had not seen the ambulance in time to avoid hitting Bowyer.
"We were all coming to pit road and I saw an ambulance sitting there," said Kenseth.
"I looked left of the ambulance at the same time [Jason] Hedlesky [Kenseth's spotter] yelled at everyone to stop, there was an ambulance just sitting there.
"It was an accordion effect and I just couldn't get stopped.
"[I'm] not really sure why pit road was open with an ambulance parked there, but everybody stopped and I didn't see it in time and ran into the car in front of me.
"It's a very narrow entry. Pit road speed is pretty fast - 45 miles an hour or something.
"Still I shouldn't have hit the car in front of me, but I can't say I was expecting to see an ambulance blocking me."
Regular season champion Martin Truex Jr described the incident as "inexcusable".
"I was thinking that whoever hits the button to open pit road needs to pay attention to what's going on on the race track," said Truex.
"It's not like it was a big surprise.
"The emergency vehicles were riding down backstretch next to us as soon as we came off of 2 and continued all the way until the opening of pit road.
"Somebody obviously wasn't paying attention or wasn't doing their job properly and in my opinion, at this level, it's inexcusable."