Re: Extra sections

"The Rights of Trains" by Peter Josserand. An excellant book about operating by train order and timetable schedule. Recently reprinted (not the best quality) by Simmons-Boardman - see www.transalert.com to order
On some branches there would be a general order or special instruction not requiring the display of white signals since all movements were extras. Other branches would not use a schedule or extra trains, but would use the staff system or block register to authorize trains. (Block Register Territory is still commonly used today)
Before I confuse anyone - The same engine could make multiple trips as an extra, but each movement would have to be individually authorized by train order. If engine 484 helped a train to Hipass and was given an order there stating "ENG 484 RUN EXTRA HIPASS TO LOWLAND"; then it could run to Lowland from Hipass - dodging any superior trains. Upon arrival at Lowland, its train order is fulfilled. If it later helped another train to Hipass, it would have to obtain a new order to return to Lowland. A train order remains in effect until fulfilled or annulled.