Danish Signaling, Automatic Block Signals

Introduction

Automatic Block Signals are rarely found on single track, due to the fact that most single track lines in Denmark see short distances between stations or/and low traffic volumes.

Automatic Block Signal Types

Logically, Automatic Block Signals are divided into advance signaling Automatic Block Signals and non advance signaling Automatic Block Signals. Non advance signaling Automatic Block Signals are found where the next Main Signal (Entry Signal or Automatic Block Signal) is preceded by a Distant Signal. Non advance signaling Automatic Block Signals are marked by a yellow plate with a black letter "F" on the mast (left).

Non advance signaling Automatic Block Signals are always the 2-lamp type. Advance signaling Automatic Block Signals on main lines are always the 3-lamp type. Almost all double track on the S-bane features the 4-lamp Automatic Block Signal type though one line features a 2-lamp advance signaling type and yet another features a mixture of advance and non advance signaling signals. Some installations vary from the rule. Automatic Block Signals and Exit Signals on the same line are  almost always the same type.

Automatic Block Signal Aspects and Indications

"Stop" (Danish: "Stop")

Stop	X	X	X	X

"Stop and Proceed" (Danish: "Stop og Ryk Frem")

Stop, then proceed to next Main Signal. Maximum speed in the next block is 60 km/h (40 mph). Next Main Signal must be expected to show "Stop"	X	X	X

"Proceed" (Danish: "Kør")

Proceed at prescribed speed	X	X	X	X
The signal does not convey information about indication on the following Main Signal (distant signal to follow)	X
Expect next Main Signal to show "Stop" (A following Entry Signal may show "Proceed" or "Proceed Through" with a permitted speed of less than 75 km/h)		X	X	X
Trains with active Cab Signal: Cab signal will govern	X	X	X	X

"Proceed Through" (Danish: "Kør Igennem")

Proceed at prescribed speed. Next Main Signal shows "Proceed" or "Proceed Through" (with a permitted speed of at least 75 km/h if next signal is an Entry Signal)	X	X	X
Trains with active Cab Signal: Cab signal will govern	X	X	X

"Conditional Stop" (Danish: "Betinget Stop") - Copenhagen Suburban lines only

Train without active cab signal: Stop	X
Trains with active Cab Signal: Cab Signal will govern	X

Automatic Block Signal Usage

Double Track Usage

Main Lines

The Automatic Block Signals are usually approach lit. The green lamps are dimmed when no train is present in the block approaching the signal. The "Stop" aspect is never dimmed:

Main and Distant Signals

Older Suburban Lines

Otherwise the functions of this system are identical to the main line system:

Copenhagen Suburban Lines

Trains are permitted to follow each other in blocks sections of so called HKT-sections (Danish: HKT-afsnit), separated by rectangular red and white signs. The Automatic Block Signals are approach lit and normally show the special "Conditional Stop" aspect, permitting trains with active cab signal to proceed:

The Automatic Block Signals switch to "Stop" when the HKT-section immediately behind the signal is occupied:

As soon as the first HKT-section behind the signal clears, the Automatic Block Signal switches to "Conditional Stop" again, permitting the next train to proceed on cab signal indication. The Automatic Block Signal displays the lit "Conditional Stop" aspect until the train passes the next lineside signal:

Trains with failed cab signal (or without cab signal) are governed by ordinary signal aspects. The line block system receives a command to switch to lineside signaling from the neighboring station interlocking. The Automatic Block Signals are then prevented from showing "Conditional Stop" for the train in question, remaining at "Stop" until an absolute block (to the next lineside signal) can be established:

The Automatic Block Signals automatically revert to normal after the passage of the train:

Once switched to lineside signaling, the line cannot be switched back to cab signal only running. So even if, say, trains are swapped, the first train will run by lineside signals. Since the wayside cab signal system is always active, however, a train with working cab signal will always be supervised by the HKT-system.

The Copenhagen Suburban automatic line block system (called type DSB 1969) features facilities for wrong main running similar to the features of the Line Block System type DSB 1954 . After wrong main running the type DSB 1969 line block system switches to the lineside signaling mode for the first train. Since the line is completely clear in this situation, and the wayside cab signaling is active, there is no loss of traffic capacity or safety.

Single Track Usage

Older Mainline systems

Multiple Track Bidirectional running

The line block has a set direction of travel, the direction being changed when a station sets an exit route for a train opposing the already set direction. Signals in the direction of travel show lit proceed aspects, opposite direction has all signals at "Stop":

On later bidirectional installations, all signals normally show "Stop". The block system still has a set direction, but the signals clear only when a train is approaching. The Automatic Block Signals then remain at "Stop" until the next train approaches.

Keeping signals at "Stop" avoids resetting signals to "Stop" when reversing traffic on a track.  The "Stop"-setting of the Automatic Block Signals has often led to an emergency braking when a locomitive engineer traveling along one of a numbr of parallel tracks is uncertain which of many signals actually went to "Stop".

"Stop and Proceed"

Most multiple track line block systems in Denmark feature the "Stop and Proceed" aspect, an important exception being the Copenhagen Suburban systems for cab signaling.

Peculiarities