When a semitrailer is parked on the shoulder of a divided highway and two flags are being used in the place of lighted lamps, the first flag should be placed:

If lighted lamps are not required to be used during an emergency stop, they should be replaced by two red flags. When a semitrailer is parked on the shoulder of a divided highway and two flags are being used in the place of lighted lamps, the first of the two flags should be placed 100 feet behind the vehicle.