LZB - Linienzugbeeinflussung (Linear Train Control)


At first I want to explain what the lengthy word means (you know, German is full of famous words like Eisenbahnschaffnerfahrkartenlocherzange [email me for a translation and win a prize]) and why LZB is used.

Linienzugbeeinflussung literally means Linear Train Control, as opposed to using fixed signals (which would be called Punktförmige Zugbeeinflussung [Spot wise Train Control], since communication to the train takes place only at certain spots, i.e. the signal locations). That would be the Indusi system.
Technically, cable loops are placed between the rails. These cables serve as antennae to send signals to the train. The train's position is still determined by block occupancy check (i.e. it is known which block a train occupies, but not where it is within that block). A more advanced technique uses radio transmission that would be called FZB - Funk-Zugbeeinflussung (Radio Train Control).

At traditional signalling, the maximum speed is limited to 160 km/h, since at that speed the brake distance is about 1 km. At larger speeds the distance between distant and main signal would have to be increased, which would make blocks longer thus lowering line capacity (apart from the investments in moving signalling equipment around).
LZB in turn monitors several blocks ahead (7000 m for a maximum speed of 200 km/h, 9900 m for a maximum speed of 250 km/h) and gives advance notice of a signal's indication.

The signalling and signal box equipment is unchanged, since LZB just overlays the block signalling system. On an LZB enabled line, all signals show their normal aspects, even when an LZB-enabled train passes through (NOTE: on newer installations this is different in some cases. See below).


The LZB monitors that signal's indications and calculates the current maximum speed. If a signal in advance (the target) would show a lower speed or even stop (the target speed), the maximum speed would be lowered, to ensure that the train will be able to meet the target speed at the target.
Simply speaking: suppose a train going at 250 km/h and some signal in advance would show stop (target speed=0), then, taking the train's braking characteristics into account, the train must lower its speed far before the distant signal at caution becomes visible, so its permitted speed will be lowered continuously.

The driver does not rely on the fixed signals (in fact they are not valid to him) but on a cab display. This display essentially shows four parameters:

V-ist Actual Train Speed
V-soll Current Maximum Train Speed
V-Ziel Target Speed
Zielentfernung Target Distance

The permitted speed usually equals the maximum train speed, unless a special order or other circumstances require a lower speed. The target speed is the speed that is to be reached at the target point, and the target distance is the distance until that point is reached.

The Cab Display


To the left you see the acceleration/deceleration meter, to the right you see the speed gauge.
The speed gauge shows three speeds:

The 'stop' aspect of traditional signalling would be given by a target speed of 0 and the respective target distance.

LZB and Signals

As said above, LZB is an overlay system, i.e. the traditional main & distant signals remain in place. When a non-LZB train passes through, signals operate as usual. When an LZB train passes through, the signals still operate as usual showing their proceed, caution, and stop aspects. The (almost) only difference is, that the train is notified of the signals' aspects way before approaching the distant signal, permitting longer brake distance and thus higher speeds.

Now on some new lines where almost only LZB trains were expected the installation of many signals could be avoided. On these lines signals are only provided at LZB starting and end points, crossings, and as entry and exit signals. The line itself is still divided into blocks (the so-called LZB blocks) which are not delimited by signals but marked by the LZB block markers. LZB-Blockkennzeichen 

So on such lines you effectively have two overlaying block systems: the LZB blocks and the blocks delimited by the signals. The latter have to be observed should a non-LZB train pass through.

There is a special case: suppose a non-LZB train has passed a signal, and is on the line already a few LZB blocks away, but still before the next fixed signal. Consequently the signal in rear shows stop. Now an LZB train is scheduled after the first train. Since the second train is governed by LZB and the next LZB block is free, it could safely pass the (red) signal into that unoccupied LZB block.

However DBAG doesn't want to stress their drivers by having them to pass red signals, and so on these lines signals are switched dark when an LZB train approaches.


CIR-ELKE is an English/German acronym and stands for "Computer Integrated Railroading - Erhöhung der Leistungsfähigkeit im Kernnetz", the latter part means "Augmenting the Capacity in the Core Net" ("Elke" is also a German female name).

On conventional lines all trains are equipped with LZB and the line itself is divided into very many very short LZB blocks. So the line capacity can be increased because an LZB train does not occupy some 1000 metres or more of line (a standard block) but just a few hundred metres. This is already used with the subways in Munich and Vienna and will be tested on DBAG lines between Basel and Freiburg.


FZB means Funk-Zugbeeinflussung (Radio Train Control). This is similar to LZB, but the information between train and signal box is not passed by wires on the line but by radio. Also and more important the position of the train is also determined by radio (as opposed to block occupancy detection devices), and the trains run with only braking distance after each other, so blocks (and consequently signals) will vanish completely on those lines. This will be tested between Köln (Cologne) and Frankfurt am Main.