For example, a flashing aspect can be used to display a less restrictive signal. In this case, if the relay that controls the flashing fails, the signal becomes more restricting. A flashing yellow, in Canada and the United States, at least on the top or middle heads if there is more than one light, means advance clear to stop (or alternatively advance approach) which means expect the next signal to be clear but not the one after. A solid yellow means clear to stop (or alternatively approach) which means expect the next signal to be stop.