The Manual Block System (MBS)

In recent years a new form of authorizing the movement of trains over relatively lightly trafficked lines has been introduced. It  was first used on the (then) Pacific Great Eastern Railway, then it moved to the CN Great Slave Lake Railway and the Northern Alberta Railways. The prairies are now well covered by MBS and it is also used in Ontario and Quebec.

In a nutshell, this is a way of issuing train orders by radio. In brief:

 there is no superiority of trains.
 the MBS clearance is the only authority for movement, except within yard limits.
all trains are designated as "extra" or "work extra".

The dispatcher transmits a MBS clearance and must write it down in a book. The recipient must repeat the clearance which is then OK'd in the normal manner. Clearances may be given for sections of trackage as designated by mileages and may also be given to foremen authorizing them to carry out track work.

A train or track unit authorized to proceed must move in the direction specified and must advise the dispatcher when it has cleared the section. A work extra may move in either direction. Two or more work extras may be authorized, to work within the same two limits protecting against each other.

This is a very flexible system that has many advantages over the timetable and train order system. The key is good radio coverage. The system can only be established over lines with continuous radio coverage. This is an added benefit to those of us who own scanners as we can obtain a better idea of train movements anticipated.

MBS may only be used on those lines so designated in the timetable. On Canadian National the following subdivisions are covered: