The FIA is investigating how a bus ended up next to the track during Formula 1 testing in Bahrain on Friday, triggering the third bizarre red flag of the week.
The final afternoon session at the Sakhir circuit was stopped after just seven minutes when a bus was spotted in front of the barriers on the outside of Turns Nine and 10.
With Alpine's Pierre Gasly, Haas's Esteban Ocon and Racing Bull's Yuki Tsunoda out on the circuit at the time, race control opted for an immediate stoppage of the session until the vehicle had moved to a safe place.
After four minutes, with the bus once again behind the barriers, testing was able to resume.
An FIA spokesman confirmed that the bus had caused the red flag, and that the matter would be looked into.
"The red flag this afternoon was for an unauthorised vehicle," the spokesperson said. "It was not on the track, but on the service road. However, it was unprotected by barriers and we did not know where it was going.
"Every track incident is thoroughly looked into and we're sure feedback will be shared with the relevant stakeholders and the appropriate actions taken."
The bus driver appears to have taken a wrong turn on a service road next to the circuit where there is a gap in the crash barriers. This area was later closed off with a fence, as the photograph below shows.
The Friday afternoon red flag meant there has been a hat-trick of slightly leftfield reasons for session stoppages this week.
On Wednesday evening, the first day of the test, track action was halted for around an hour after the Sakhir circuit suffered a full blown power outage.
F1 later explained that the problem had been caused by a problem with an external substation failure.
Earlier on Friday, the morning session had to be halted after shattered glass from a trackside gantry on the start/finish straight fell on to the circuit and had to be cleaned up.
It was suspected that the glass panel had been broken after a stone was flicked up by Haas driver Oliver Bearman, who was unaware at the time that it had happened.
Asked by The Race if the theory was correct about the stone coming from his car, Bearman said: "So I've heard. I feel really bad now, but of course it wasn't aimed. But, yeah, apparently I was the one who smashed the window."
