Green flag is waved at the following observation post of the observation post where yellow flag is waved. Green flag means the end of the yellow flag zone. Also it used as a signal to start a session or resume a race. The display of green flag is performed by waving.
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Regulations
End of the yellow flag zone
When yellow flag is waved, green flag is waved at the following observation post, it means the end of the yellow flag zone. Yellow flag zone is the section from yellow flag to green flag.
When yellow flag is waved, green flag is waved at the following observation post to notify the driver that the course is clear.
Formation lap
In case the start of the race is a standing start format, a formation lap is conducted before the start of the race. After compeleting one lap of the course on formation lap, all cars returns to the own grids. During the formation lap, green flag is waved at all observation posts.
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Green flag is waved before standing start
At the start of a standing start format, green flag is waved behind the grid when all cars have arrived on the own grid. After this, the red signal for the start is illuminated by the starter.
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Green flag is waved when the safety car is removed at the restart of the race
When ending the safety car, the safety car pits in to restart the race, yellow flag and SC board that has been displayed at all observation posts is removed. Instead, green flag is waved to notify the driver of restart the race. Green flag is removed when all cars pass the control line.
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Operation as local rules
As a local rule specific to the circuit, green flag may be waved on all observation posts at the start of free practice or qualifying session. This is performed to notify the driver of the location of the observation posts, and green flag is removed after the leading car completes one lap.
On motorcycle race such as MotoGP, regulations require that green flag is waved at all observation posts at the start of free practice or qualifying session.
2.5.5.1 f) Green flag
This should be used to indicate that the track is clear: it should be waved at the marshal post immediately after the incident that necessitated the use of one or more yellow flags.
It may also be used, if deemed necessary by the Clerk of the Course, to signal the start of a warm-up lap or the start of a practice session.