Acceptance Lever working (AL) is a method of operating a single line railway without the use of tokens or staffs. It relies on the section being Track Circuited throughout, with permission for trains to enter the line being given by the use of a special Acceptance Lever, that releases the signal allowing entry to the section at the other end. The Acceptance Lever is locked when a train is detected in the section by the track circuits, preventing it from either being pulled to release the signal into the section, and also from being returned to the normal position whilst a train is still travelling through the section (the signal may only be cleared once). Additionally, if the Acceptance Lever at one end is reversed (to allow a train to pass in one direction), the lever at the other end is locked, preventing permission being given for a train to proceed in the opposite direction.
Method of operation
The signalman sending a train will alert the receiving signalman with the "Call Attention" bell signal, and when he or she responds will, by bell signal, ask "Is the line clear for [this kind of train]", there being different signals for different train types. If the receiving signalman accepts the train, he or she will repeat the signal back, and will reverse the Acceptance Lever. An indication is given in the other signalbox to indicate that this has been done.
Reversing the Acceptance Lever at the receiving end will unlock the signal which allows trains to enter the section of line between the two signalboxes at the sending end. The signalman will clear this signal, which is the only permission that trains need to enter the section. As the train departs, the sending signalman will check it is showing the correct tail lamp at the end of the train, and send the "Train Entering Section" bell signal to the other signalman. During the time that the train is in the section, the signalmen at either end are reminded of its presence by track circuit indications in each signal box, and by either the reversed Acceptance Lever in the receiving signal box or by the associated indication in the sending signal box.
When the train arrives at the second signal box, the signalman will return the Acceptance Lever to the normal position once the train has passed his signal protecting entry to the section in the opposite direction, and send the "Train Out Of Section" bell signal to the sending signalbox. Unlike Electric Train Token working, there is usually no requirement to see the tail lamp before doing this, as the track circuits prove to the signalman that no part of the train has been left behind in the section (although for certain types of non-passenger trains, where the risk of the track circuits falsely showing "Clear" is judged to be higher, the requirement to observe tail lamps is still in place).