Once all the cars have formed on the grid, after the medical car positions itself behind the pack, a light system above the track indicates the start of the race: five red lights are illuminated at intervals of one second; they are all then extinguished simultaneously after an unspecified time (typically less than 3 seconds) to signal the start of the race. The start procedure may be abandoned if a driver stalls on the grid, signalled by raising his arm. If this happens, the procedure restarts: a new formation lap begins with the offending car removed from the grid. The race may also be restarted in the event of a serious accident or dangerous conditions, with the original start voided. The race may be started from behind the Safety Car if officials feel a racing start would be excessively dangerous, such as extremely heavy rainfall. As of the season, there will always be a standing restart. If due to heavy rainfall a start behind the safety car is necessary, then after the track has dried sufficiently, drivers will form up for a standing start. There is no formation lap when races start behind the Safety Car.