Bu Signals

Grade Crossing Signals

Introduction

These signals are installed at grade crossings on the DB, where they are known as Bahnübergangssignale. Different types and combinations of signals may be used at a crossing, depending on its location. On main lines, crossings are well-protected by the Bü0/1 overseeing signal (Überwachungsignal) and an integrated safety system (called Indusi) that can automatically stop a train before it enters an unsecured crossing. These are referred to as "Üs" or "Lo" (lokführerüberwachten) crossings, since they are equipped with overseeing signals from which the engineer (lokführer) receives feedback and responds accordingly. On secondary lines with lower speeds, crossings may not have any overseeing signals or fail-safe braking systems. They are usually monitored by the drive service manager of a local station, and are called remote-overseen (fernüberwachten) "Fü" crossings.

Both types of crossings have road signals and, in most cases, gates to warn vehicles that a train is approaching. These are activated by a mechanical or inductive switch contact next to the track that is closed by an approaching train far in advance of the crossing. At Üs/Lo crossings, the same switch activates the overseeing signal as well, and its location is marked by a Bü2 board that also announces the upcoming signal. Since Fü crossings do not have overseeing signals, the switch position is marked with a Bü3 board, which also warns the engineer that the crossing is not protected by a signal.

Additional special-case signals exist to indicate a reduced distance between an overseeing signal and a crossing, as well boards that announce and mark the kilometric position of one or multiple crossings. Where a small station or Stop (Halt) is located between an overseeing signal and a crossing, a second signal is usually installed just before the crossing and is marked with a "repeater" signal board. There are also signals that instruct the engineer to warn the vehicle traffic that a train is approaching, such as the Bü4 whistle and Bü5 ring boards.

Signal Descriptions

Bü0 Stop Before Grade Crossing - Installed on main lines ahead of grade crossings with automatic fail-safe braking systems. This signal aspect indicates that the rail switching contact was not activated properly by the train and the crossing is not secure. The train must stop before the crossing, and the engineer must then either manually switch the crossing with a switching key (Handeinschalttaster) or drive slowly over an inductive sensor that will switch it automatically. The second type of crossing is marked with a sign that reads "Automatik-HET" (Hilfseinschalttaste), meaning "automatic assisted on-switching."

Bü1 Grade Crossing Clear - Same as Bü0 above, except with a blinking white light. Indicates that the train has activated the rail contact properly, the crossing is secure and may be passed.

Bü2 Diamond Board (Rautentafel) - Installed on main lines ahead of grade crossings with automatic fail-safe braking systems. The first board, with 4 diamonds, announces to the engineer that there is an upcoming grade crossing signal, which must be observed as aspect Bü1. This board also marks the location of the rail switch contact that activates the crossing signals. In newer installations, this board may be followed by three additional boards, spaced 75m apart, to improve the recognition of the signal.

Bü3 Contact Marker Board (Merktafel) - Used with remote-monitored "Fü" (fernüberwachten) grade crossings only, which are not equipped with Bü0/1 signals or automatic braking systems. Indicates the location of the switch contact that activates the roadway crossing signals.

Bü4 Whistle Board (Pfeiftafel) - Blow whistle for approx. 3 seconds. Board background may be either white or black. If there is a Stop (Halt) between this board and the grade crossing, the board will also have a striped sign above it. It then applies only to through trains. A second board will be placed directly after the Halt that will apply only to trains that had stopped.

Bü5 Ring Board (Läutetafel) - Ring bell. This board is installed at crossings without heavy vehicle traffic. The engineer must ring the bell until the front of the train has reached the crossing. If there is a Stop before the crossing, the board will also have a striped sign above it (see Bü4 above).

Repeater Signal Indicator - Mounted below the mast plate on a Bü0/1 signal to indicate a repeater signal. A repeater may be installed directly before the crossing if there is a stop point between the primary signal and the crossing.

Reduced Distance Indicator - Mounted below the mast plate on a Bü0/1 signal to indicate a reduced braking distance to the crossing.

Announcement Board (Ankündigungstafel) - Placed at the switch contact location for the crossing signals, this board announces the kilometer mark of the upcoming crossing.

Indicator Board (Kennzeichnungstafel) - Placed directly before the crossing, and indicates its location at the kilometer mark noted on the board.

Multiple Crossing Indicator Board - The "Bü/Bü" board (left) tells the engineer that multiple closely-spaced crossings are served by the same rail switch contact. It is installed above the announcement board for the first crossing (at the location of the contact). At the first crossing, the white indicator board will also have a yellow announcement board below it for the next crossing. The last crossing will have only a white indicator board.

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