This type of restriction, called an ESR, applies to cases where there has not been enough notice to list the restriction in the weekly operating notice. If trains cannot be diverted to another line, signallers must stop the trains and explain the circumstances to the drivers, who must not exceed 20 mph through the section. Warning boards, speed indicators and termination indicators are set up in the same way as TSRs, in addition to which an emergency indicator must be placed 200 yd in rear of the warning board. Emergency indicators are rectangular boards with black chevrons pointing upwards and two flashing white lights.