<P> In Formula One, all lapped cars between the leaders are permitted to advance one lap . </P> <P> The rule, as enforced in the three open - wheel series, is designed to prevent lapped cars from blocking on ensuing restarts, as to prevent unsportsmanlike blocking when a lapped teammate or friend of one driver attempts to help that driver through impeding the progress of an opponent on the restart . </P> <P> The yellow flag with vertical red stripes is displayed stationary at local flag stations to indicate that track conditions have changed due to substances on the track which could reduce grip or cause a car to lose control . Generally oil, coolant, small pieces of debris or sand are the hazards . It can also be "rocked" back and forth (but not waved) to indicate a small animal on the racing surface . Many organizations will display this flag for only two laps, after which the changed surface is considered to merely be "part of the track". </P> <P> The solid red flag is displayed when conditions are too dangerous to continue the session . Depending on the series and the circumstances, the cars are typically directed to proceed immediately to pit road, or to stop at a specific spot on the track . In some severe cases the cars might be required to stop immediately where they are . During red flag conditions, repair work in the pits or garage area is typically prohibited, except in non-points paying races . </P>

What does a red and yellow flag mean
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