ABT is a rack railway system. It was used in Tasmania but also other parts of the world but being Aussie I only know about Tasmania. If you do not know what a rack railway system it is use to run loco's/trains up steper graduatents than most railways would go. If you do an internet search for rack railways I am sure you will get lots of information.
Paulz Trainz has produced a ABT loco to run with it but it is payware.