Blue flags and lapped cars
A waved blue flag tells a driver that a faster car is right behind them and wants to get past. What the driver has to do depends on the session.
- In practice and qualifying, it's a warning: a faster car is close behind and about to overtake. The driver should move out of the way, but the main rule here is about not impeding (see below).
- In the race, it's shown to a car that is about to be lapped, meaning it's a full lap behind the car coming up to pass it. That driver must let the faster car through at the earliest opportunity.
Blue flags aren't shown to cars that are racing each other for position. If two cars are on the same lap, it doesn't matter how much quicker one of them is.
How blue flags are shown
Marshals wave blue flags at their posts, and the same signal appears on the trackside light panels and on the driver's steering wheel display. In F1 the timing system works out when a car is about to be lapped, so the warnings appear automatically as the gap closes. The team will also tell the driver on the radio.
A stationary blue flag, or a flashing blue light, is also used at the end of the pit lane. That one is for drivers rejoining the track, to warn them that cars are coming. See lights, panels and pit exit signals.
What "earliest opportunity" means
The lapped driver doesn't have to pull over in the middle of a fast corner. They are expected to let the faster car past at the next sensible point, usually by lifting slightly on a straight or leaving the racing line open into a braking zone. Most drivers do this without fuss because it costs them less time than fighting.
The stewards look at how many blue flags a driver ignored and how much time the faster car lost. There is no fixed number of flags that triggers a penalty, but if a driver holds up the leader for several corners or more than a lap, they are likely to be investigated. The usual punishment is a 5-second time penalty, sometimes with penalty points.
Lapped cars and strategy
Traffic plays a big part in race strategy. A leader who catches a group of backmarkers can lose a second or more getting through, which can open the door for a rival to make an undercut work. The lapped drivers are also allowed to fight each other while letting the leader through, which can make things messy.
Blue flags can be awkward for a lapped driver who is fighting another lapped driver. They have to give way to the leader without losing their own position, and sometimes they don't manage both.
Impeding in qualifying
In qualifying, the more important rule is about impeding. A driver on a slow lap who gets in the way of someone on a fast lap can be penalised, even if no blue flag was shown. The usual penalty is a drop of three places on the grid. Teams are expected to warn their drivers on the radio when a fast car is coming, so a missed warning is the team's problem as well as the driver's.
Unlapping behind the safety car
Under the safety car, race control may send the message "LAPPED CARS MAY NOW OVERTAKE". The lapped cars then pass the leaders and the safety car to get back onto the lead lap, and rejoin the back of the queue. This keeps lapped cars out of the way of the leaders when racing restarts. The rules on which cars may do this, and when, were tightened after the 2021 Abu Dhabi Grand Prix.