Signal FAQ: Manual Block Working in Germany

Manual Block Working in Germany

Joern Pachl


Although modern lines in Germany are usually eqipped with automatic block systems with line clear detection devices there are still older installations using the traditional German manual block. The German manual block system works with special block instruments. In German such a block instrument is called a "Blockfeld". In difference to British practises the German block instruments are always "block and lock" instruments, e.g. they are interlocked to the signals. As long a block section is occupied by a train all signals which may govern train movements into this block section are locked by block instruments.

A block instrument has two positions, "blocked" and "non blocked". Both ends of a block section are equipped with corresponding block instruments which are electrically connected. One of two corresponding instruments is in the "blocked" and the other in the "non blocked" position. A "non blocked" instrument can be operated to the "blocked" position by pushing a block button. At the same time the corresponding instrument changes from "blocked" to "non blocked" position. A "blocked" instrument can only be released to "non blocked" position by operating the corresponding block instrument. A block instrument has a block indicator that shows a red sign if any signal is directly or indirectly locked by the instrument. Otherwise it shows a white sign. Corresponding block instruments usually show the same sign (exception: block instruments for opposite locking).

Every block section has an entrance block instrument which is interlocked to all signals which govern train movements into the block section (block signal or exit signals of an interlocking) and locks these signal if the block section is occupied by a train. The entrance block instrument corresponds to an exit block instrument at the other end of the block section. The exit block instrument is interlocked to the signal at the end of the block section and is equipped with an electric lock (so called "clearance lock") that prevents operating the instrument until the train has operated (occupied and cleared again) a a short track circuit (usually combined with a rail contact) behind the clearance point (end of overlap) of the signal.

On single lines there are separate entrance and exit block instruments for each direction. In addition the interlockings at both ends of a single line are equipped with so called "permission" block instruments to prevent opposite movements by opposite locking of the exit signals.

Infrastructure examples

Meanings of the abbreviations used in the drawings:
ABB meaning German term
EN entrance block instrument Anfangsfeld
EX exit block instrument Endfeld
P(OL) permission block instrument (for opposite locking)
CL clearance lock Streckentastensperre

Example 1

Double line between two interlockings without intermediate block signals:

Example 2

Double line between two interlockings with intermediate block signals:

Example 3

Single line between two interlockings with intermediate block signals:

Sequences of block working

Double line working

Operator A cleares signal N3 for a train.

After train has passed signal N3 it is reset to stop position and the signals N1,2,3,4 are automatically locked by a rotation locking device in stop position. Thus it is impossible to clear one of the exit signal again even if the operator doesn't properly operate his block instruments. Operator A sets his entrance block instrument to "blocked" position thus locking his exit signals with the block instrument. That way the corresponding exit block instrument at interlocking B gets in "non blocked" position. Both block instruments are now showing a red sign. So the operator B can see that a train has occupied the block section and cleares signal A.

When the train has passed the signal A and has occupied and cleared again the short track circuit at the clearance point the clearance lock unlocks the block button of the exit block instrument. The clearance lock shows a white sign. After signal A is reset to stop position it is now possible to operate the exit block instrument. But operator B is only allowed to do this if he has checked train integrity by watching the rear end train marker.

To clear the block section operator B operates his exit block instrument to "blocked position". So the entrance block instrument in interlocking A gets to "non blocked" position and the exit signals in interlocking A are unlocked. The block signs on the instruments changes to white and the clearance lock also gets to normal position locking the block button of the exit block instrument. Now operator A may clear an exit signal for a another train.

Single line working

The entry and exit block instruments are operated the same way like in double line working. In addition the interlockings A and B are equipped with corresponding permission block instruments. In the interlocking where the permission block instrument is in "blocked" position all exit signals to the line are locked in stop position. So the position of the permission block instruments determines the current of traffic. When the current of traffic should change the operator with the "non blocked" permission block instrument blocks his instrument so the corresponding permission block instrument is unlocked. As long the current of traffic is not changed there is no need to operate the permission block instruments.

Example: The actual current of traffic is from A to B. Train X is approaching interlocking B where train Y is waiting for departure to A. The block signal is locked in stop position by the "blocked" entrance block instrument at the block station. All exit signals in interlocking B are locked in stop position by the "blocked" permission block instrument.

Train X has arrived in interlocking B. The operator has cleared the block section by operating his exit block instrument. If the full line is clear, e.g. all entrance block instruments of the line are "non blocked" it is possible to change current of traffic by operating the permission block instruments. If only one entrance block instrument is "blocked" the electrical current for the permission block instruments is interruptet to prevent dangerous changing the current of traffic. Thus it would be dangerous, if the operator of the block station forgets operating his entrance block instrument after the train has passed. In such a case it would be possible to change the current of traffic even if there is a train on the line. To prevent this at intermediate block station the block buttons of entrance and exit block instruments of the same direction are mecanically connected. So it is impossible to clear a block section by operating the exit block instrument without blocking the entrance block instrument for the section ahead.

Operator A operates his permission block instrument to change the current of traffic. Now the exit signals in interlocking A are locked and the exit signals in interlocking B are unlocked. Operator B can now clear signal P3 for train Y.

Text: Joern Pachl
HTML: Mark Bej