Railway Signals in Goyanes

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A modern 5-light signal displaying the "High Speed Clear" aspect. This allows the train to proceed above 130 km/h following cab speed signals.

Railway signals in Goyanes evolved from electro-mechanical semaphores that changed position to indicate track block status. Before then though, railways employed “track officers” to manage sections of track using hand gestures, line-of-sight techniques, and physical tokens that had to be passed from train to officer and vice versa. This was wildly inefficient, and as the railways grew, technologies were developed to reduce collisions and improve railway safety. Starting with the Grand Trunk Railway and spreading quickly around the nation, electric track circuits that controlled semaphore signals began to take hold. The process started in the 1870s, but by the 1890s, Goyanes’ railway network was fully electro-mechanically signaled.

In 1885, the Stortoghass Tunnel Crash in Gojannesstad occurred, where a through train engineer running a service from the Hysende-Osanhalt-Kongsland Railway onto the grand trunk in Gojannesstad became confused by the Grand Trunk's signal system, and crashed the train, resulting in 30 deaths and more than 50 injuries. This caused the Ministry of Transportation (then known as the Ministry of Railways) to mandate a new, unified, national signal system. The new signal system became known as M-Class signals (M-klassesignalen). M-Class signals used semaphores and relays, and a unified set of meanings. This helped promote inter-operation, and created a stanrdized and safer working environment for the railways.

By the early 1930s, the Ministry of Railways had consolidated all of Goyanes' railways into four companies, the Grand Trunk, the Hysende-Osanhalt-Kongsland, the Nordstrom Seabord, and the Hirendag Road. However in 1921 a fatal accident caused the Ministry of Railways to mandate the four lines to install train protection systems. The system invented by the Grand Trunk Railway and Nasjonalsignalen, ATB, became the most popular, as it provided full cab signalling, and beginning in 1930, was installed on main lines in Goyanes. As color-light signals began to see widespread use during the consolidation era, the system was standardized to fit the ATB system and provide complete unification of teh stafety ststem.

The devolopment of the HHT system in the 1960s and 1970s forced Gojan Jårnbaner, Goyanes' state railway operator, to develop a new cab signalling system. The high speeds of the HHT system prevented operators from being able to see and comprehend any trackside signals, so a system that transmits not just speed like ATB, but track information directly to the driver was created, known as AVK. AVK is currently on its second iteration. In addition, a new system known as ATS-V that uses train-mounted electronics and track-mounted transponders to enforce red signals, confirm yellow and double yellow signals, and stop a train if it is running too fast before a red signal. ATS-V is installed on all classic lines in Goyanes.

Currently in Goyanes, all signals are cab-only or color-light, all classic lines and trains are equipped with ATS-V, and high-speed trains and lines are equipped with AVK.

Fixed Signals

Signals in Goyanes use a combination of route and speed signalling that has evolved over time from the previous semaphore system.

Main Signals

Main signals (Hovedsignalen) are called so because they protect a section of track, known as a block. The main signal protects the entrance to the block of track is guards. There are three types of main signal in Goyanes, starting signals, home signals, and block signals. These three types of signals are governed by two different regimen of signalling practice, automatic block signals and non-automatic block. Automatic block means the block is protected by a simple circuit that detetcts a train inside a block and automatically changes aspcects to block access to that section. When the train leaves the block, the block is automatically opened up again. Non-automatic block means that signals must be lined up by a dispatcher manually ahead of time. Typically interlockings are protected by non-automatic block signals and sections between interlockings are protected by automatic block signals. However, under the non-automatic block system a starting signal has no protected section; it only indicates that all turnouts on the route to the mainline are switched correctly. Under the non-automatic block system trains cannot leave a station without an appropriate token, even if the starting signal is clear. This token is usually a separate light that activates when the stationmaster who controls that block allows the train to pass through the interlocking.

All main signals in Goyanes have between two and six lights, that are either red, yellow, or green. Two-bulb signals may have either green or yellow, but must have red.

The following graphics show main signals. In addition, the main signals shown have the capability of displaying all aspects. In most circumstances, main signals can only display certain aspects that relate to the condition of the lines they protect, and as such could have as few as two lamps, instead of the five pictured here. A note, 5-bulb signals cannot display both high speed clear and restricted aspects. However, 6-bulb signals can display all aspects, in which case the green lamp occupies the top slot. Regardless, the light and color combinations carry the meaning, not the total amount of bulbs on the signalhead.

Aspect	Name	Description
	High Speed Clear (Hastiket Vortsette)	The high speed clear aspect is used on certain lines when trains become authorized to travel over 130 km/h. It is also interlocked with other signals so that there are at least three clear blocks ahead, unlike the usual two that a normal clear signal provides.
	Clear (Vortsette)	Proceed at the maximum authorized track speed, or 130 km/h if the track speed limit is higher. There are at least two clear blocks ahead.
	Reduction (Verminsken)	The aspect is flashing. It is used to indicate a speed limit of 100 km/h, usually to slow trains down from high speed. There are at least two blocks clear ahead.
	Limited (Begrenset)	Displayed when the next signal displays restricted speed (YY) (or caution (Y), in the case of a short block section or poor visbility of the next signal). The speed limit is 60 km/h. There are at least two clear blocks ahead.
	Caution (Advarsel)	Displayed when the next signal displays stop. The speed limit is 40 km/h. Sometimes the block ahead maynot be displaying stop if the block clears up, but the driver should never expect anything better than stop.
	Restricted (Smal)	Displayed when the distance to the next signal is unusually short, another train is running in advance of the signal or the safety overlap at the next signal is shorter than normal. The speed limit is typically 30 kmh.
	Stop (Stanna)	Not to be passed. If it is an automatic block signal, non-blocking operation is allowed, where train can continue at a maximum speed of 15 kmh after approval from the dispatcher.

If a signal lamp burns out, it will automatically switch to the stop aspect. A signal with all lights shut off should be treated as a stop sign unless there is a decomissioning sleeve on the signal, an "X" shaped board on the signal, or if it is turned to the side to face away from the tracks. Additionally, GJ mandates at least two bulbs be off between on bulbs, which is why there ends up being multiple yellow bulbs when there's ore than three bulbs on a signal.

Home Signals

Home signals (Hussignalen) permit trains to enter the station or interlocking. A home signal is absolute; therefore, non-blocking operation is always prohibited. Some stations have multiple home signals, due to station layout. In these cases, each home signal has an identification number which is counted from the outside of the station. In high-traffic areas, some operators install home signals in the center of a platform track to divide the block section. Some operators treat such signals as block signals. In non-interlocking stations, there may be a No.0 block signal instead. Home signals protecting stations usually have a "TH" plate under the signal, and those protecting interlockings usually have a "KREUSS" plate under the signal.

Starting Signals

A starting signal (Utgangsignalen) permits trains to depart the station, and is an absolute signal. In some stations, there are multiple starting signals due to station layout. In such cases, each starting signal has an ID number which is usually the same as the track number. In non-interlocking stations, there may be a block signal instead of a starting signal.

Block Signals

A block signal (kreissignalen) begins a block section in an automatic-block system. In non-blocking operation a train can proceed past a block signal after stopping for one minute at the signal and contacting teh dispatcher, even if the signal is "stop".

Each block signal is identified by an identification number; as a train travels to the next station or interlocking, the ID numbers count down. The last block signal before the home signal is number one. Each signal is associated with the next one; therefore, it cannot be manipulated by dispatchers or signalmen, unless there is a computerized central traffic system such as in Gojannestad or Naderfjord (ATN). The signal display depends on the presence of a train in advance of the signal and the display of the next signal.

A block signal is a permissive signal, so non-blocking operation is allowed. A train can continue at a maximum speed of 15 km/h after stopping for one minute and contacting dispatch before a block signal displaying stop. The train must not increase speed over 15 km/h until it arrives at the next main signal. Some lines do not require a dispatcher to be alerted before proceeding past a block signal displaying stop, if they have waited for a full minute.

A No. 0 block signal at the platform of Grønmark Station in Gojannesstad displaying the "limited" aspect.

At crowded stations on high-traffic lines, a platform track may be divided into two block sections so a following train can enter the track soon after the preceding train has departed. This signal is known as a No. 0 block signal. GJ treats this signal as a part of its home signals. At non-interlocking stations of GJ, the last block signal before the station is treated as a No. 0 block signal and known as the "home equivalent block signal." This signal is not absolute, since (unlike home signals) non-blocking operation is permitted. On ATN (Automated Train Operation Network) lines in Gojannesstad and other major urban areas, block signals are numbered serially, regardless of non-interlocking stations. In this case, some block signals are defined as home-signal equivalent or starting-signal equivalent using the corresponding plate below the signal.

Call-On Signals

Normally, only one train can enter a block section for safety; however, with this rule a train cannot be coupled with another train. A call-on signal (Spesiellingangsignalen) permits a train to enter a section already occupied by another train to enable coupling.

A home signal protecting a station with a shunting signal underneath the main signal displaying stop. The single bulb under the main signal is for route signalling.

A call-on signal is installed under a home or shunting signal. The train guided by a call-on signal can proceed under 15 km/h (30 km/h if instructed bt ATB) until it reaches the next train train. In stations where two trains use the same track simultaneously, call-on signals are required to allow two trains on a single block section. However, this is unnecessary if the platform track is divided into two block sections as discussed previously.

When calling-on is allowed, the white lights are activated diagonally. When calling-on is not allowed, the white lights are horizontal.

Route Signalling

As previously mentioned, Goyanes uses a combination of speed and route signalling. The route signalling aspect is mostly seen around interlockings. A signal protecting an interlocking will usually have two signalheads offset and at different heights. The upper signal displays information for the main route, and the lower signals display information for the diverging routes on their respective sides.

A home signal announcing the center track may take the right diverging route at posted speed, leading to track three at the station.

Especially when leading into stations or more complex interlockings, the home signal may be preceeded by signals that have two horizontal white lights underneath the signal. These are nown as "advance route setting signals." These show which diverging route is set at the next signal. If both lights are on it means the main route is set, and if only one light is on it means the diverging route is set on the respective side. These signals may also have an electronic board that displays a number, this indicates the track the diverging route leads to inside the station. Number boards are sometimes installed at the home signal as well to emphasize which track the route is leading to.

A home signal announcing track 10 can proceed via the left route prepared to stop at the next signal.

An Advance route setting signal displaying the right route is clear at the next block.

Due to space constrictions, multiple signalheads may not be available at a home or starting signal, so a more compact "route identifier light" will be placed under the signal. It comprises of white lights arranged in a "T" shape that indicate which direction the diverging routes are set to. When all lights are off it indicates the main route is set.

Shunting/Dwarf Signals

Shunting signals, also known as “dwarf signals” (kleinesignalen), are used for shunting purposes in yards. They are smaller in size, and use only white aspect colors. They may be placed on top of a half-height post, or placed at the same height as the trackbed.

Signal		Meaning
	Danger	The signal must not be passed without radio permission from dispatch.
	Movement Allowed	Movement is allowed. All points and derailers have been set. The track ahead is clear. Speed limit 30 km/h. This aspect is commonly used to allow permittivity of a signal at danger.
	Movement Allowed with Caution	Movement is allowed Points and derailers are in the right position. The track is not clear however. Speed limit 20 km/h. This aspect is commonly used to allow permittivity of a signal at danger, specifically to couple/shunt trains already in a platform or a siding track. The train must come to a complete stop before continuing.
	Movement Allowed Check State	Movement is allowed All points and derailers may not have been set. Driver must ensure all points are set as well as clearance ahead. This aspect is used to grant entrance into yards with manual track points and no electronic control.

Railroad Crossing Status (RCS) Signals

A main RCS signal displaying "Crossing Not Secured/Danger"

RCS signals (Vagersignalen or VS) are used to indicate to the driver the status of a railroad crossing ahead on the line. Various factors affect the aspect displayed. The most simple kinds simply confer if the gates are closed and locked, but the most advanced types rely on sensors that can detect if vehicles are stalled on the crossing, in addition to detecting whether or not they have been locked. There are two types of RCS signals, just like color-lights, they are Main Signals and Distant Signals. Main RCS signals are identified by a “V” sign under the bulbs. Distant RCS signals are identified by their shape and unique bulb layout.

A related signal called a Bridge Status Signal (Bryggesignalen or BS) uses the same signalheads and aspects, except the main BSS signals have a "B" signpost under the signal head, similar to how main RCS signals have a "V" signal on them.

Main RCS Signals (Hovedvagersignalen/HVS)

Signal		Meaning
	Crossing Not Secured Danger	The crossing is not secured, the train must attempt to stop before the crossing. Emergency brake application is acceptable.
	Crossing Secured Proceed	The crossing is secured, proceed normally.

Distant RCS Signals (Vørvagersignalen/VVS)

Signal		Meaning
	Expect Crossing Not Secured (Crossing not clear)	The Main RCS signal is at danger, the driver must slow the train down immediately and attempt to stop before the crossing. Emergency brake application is acceptable.
	Expect Crossing Secured (Crossing clear)	The Main RCS signal is showing secured, proceed normally.

AVK System

The orange sign indicating a non-permissive track block at the end of a train station.

The AVK system was invented in 1959 and inplemented in 1964 for use on HHT high-speed services, as operators would not be able to read and interpret lineside signals at high speed. AVK-1 was the first iteration of the system invented, with the second and current iteration being known as AVK-2. Signaling information is instead transmitted to the train and displayed as part of the train controls. The driver is shown the safe operating speed, displayed in kilometers per hour. The late-1990s-developed AVK-2 system transmits more information than traditional signalling would allow, including gradient profiles and information about the state of signaling blocks much further ahead. This high degree of automation does not remove the train from driver control, although there are safety mechanisms that can safely bring the train to a stop in the event of driver error or incapacitation.

History

The AVK system was developed by Gojan Jårnbaner engineers in conjunction with the Nasjonalsignalen company, which currently markets the system worldwide. The system was based off of ATB, a proven system that has been installed on conventional lines since the 1930s. The AVK-1 system went online in the first section of the HHT system to open, the Gojannnesstad-Naderfjord high-speed railway.

AVK-1 was a relay-based system that used rigid blocks, and communicated with the train using pulse codes sent to the train based on the signal state. The pulse codes are sent theough the front axle of the train as it bridges the circuit across the two rails, and the pulse code is interpreted by a sensor on the train, which otputs a maximum permitted speed based on the track limits and the block status ahead. In this aspect it is extremely siilar to ATB. However, as the train slowed down, the rigid block system caused an uncomfortable braking experience, which required lowering speed, then easing off the brakes, then braking harder again. This, among other things, prompted the development of AVK-2.

By 1999, the engineers decided to improve the AVK system with new microprocessors both onboard and trackside, and a new, more computerized trackside system. The new system was called AVK-2. AVK-2 was marketed by Eindrisson engineers as part of a multi-tiered approach. AVK-2 would be standard operation (cab signalling and automatic train protection from overspeed and stop signals), AVK-2.1 (optional automatic train control), and AVK-2.2 (fully automatic operation).

In 2010, the AVK system was applied on certain classic lines to test throughput capacity. It proved successful and now, certain very-high capacity lines have had the AVK-2 system installed to increase frequency of trains.

Implementation

In AVK-2, the track is dotted with transponders mounted in the center of the track every usually 200m to 1 km (in some schenarios they can be as close as 10 meters, such as at where a side track joins a main line). The sections of track block are guarded by transponders at both ends, but there are usually transponders inside the track block as well. The track block uses a standard track circuit to detect the position of a train. Lineside equipment stations transmit the last updated distance to the next train to the train via the transponder, as well as the maximum permitted line speed.

An old-style transponder coil located along the platform at Ingolfur Station. These models are compatible with the new ones, but are being replaced.

There is a main equipment box that controls about 10 blocks, which in turn is controlled by the central control room for that line. The central control room is able to integrate the AVK-2 system with the scheduling system to maintain precise headways, and ensure safety of operations.

Onboard the train, as it passes over a transponder, the distance to the train ahead, maximum line speed, and track gradients are recieved, and this information is sent to the onboard computer, which determines a braking curve using the given information and known information such as train acceleration and braking performance. The computer then displays an authorized speed on the dashboard. The authorized speed is constantly being recalculated, as the train estimates its position to the train ahead, and along the line (for gradient purposes) using the onboard odometer. The distance is confirmed/reset every kilometer when the train passes over a transponder, which subsequently updates the train on its current position.

When the train reaches the point where the computer determines it should begin braking, or if it passes a transponder and an updated speed is given, an alarm sounds in the cab which the operator must confirm. Then the braking curve begins. The operator should brake normally, but keep an eye on the speedomoeter, as the speed limit decreases in real time. If the speed of the train exceeds the maximum authorized speed, either while cruising or braking, the train will apply brakes to bring it below the authorized speed. The continuously dynamic braking curve drastically improves passenger comfort, and allows for closer headways. Once the authorized speed stops decreasing, a bell sounds in the cab.

A lineside equipment station on the Nyhett Valley High Speed Line. An new-style AVK transponder is visible in the lower right in the track.

The signalling system is permissive; the driver of a train is permitted to proceed into an occupied block section without first obtaining authorisation. An occupied block section is indicated on the speedometer by a speed limit of 30 km/h. When the speed limit is 30 km/h, the train cannot exceed 32 km/h, and must stop before any obstructions, track defects, or trains ahead. Non-permissive blocks, such as at entrances and exits to stations, and at interlockings, are marked with an orange, diamond-shaped, board with a black cross. There will always be a transponder protecting the block, as well as a dwarf signal. If a driver encounters a non-permissive board, they must do two things. First, they must check the speed indication. If it is not 30 kmh, they may proceed as normal. If 30 km/h is given, they must look at the dwarf signal at the non permissive sign, if it displays stop, they must stop before the board, and if it displays proceed or proceed with caution, they can pass the board. Entering a non-permissive block at danger will trigger an emergency brake application. Non-permissive blocks can also be guarded by a single color-light, as is the case on newer tracks. If the section is protected, a red light will illuminate. GJ has been swapping the dwarf signals for color lights since 2010 as they offer improved visibility.

A dwarf signal protecting a non-permissive track section. The light above the dwarf signal is the new color-light which has replaced the dwarf signal.

The additional information passed along by the transponders can concern a variety of events or actions, such as signal system changes at the entry or exit of a high-speed line, arming or disarming the AVK-2 system, closing air vents before entering a tunnel at speed, raising and lowering the pantographs, or changing the supply voltage at system barriers. When trains enter or leave the high-speed line from classic lines, they pass over a ground circuit which automatically switches the driver's dashboard indicators to the appropriate signalling system. For example, a train leaving the high-speed line onto a classic line would have its AVK signalling system deactivated and its traditional ATS (automatic train stop) and HBK (automatic speed control) systems activated by the train's onboard computer at the boundary point.

Oversight

A "black box" similar to an aircraft flight data recorder, passively watches over the entire process, monitoring a variety of parameters and recording the events onboard the train. In AVK-2-equipped trainsets, older paper-strip recording equipment has been replaced by a digital recording system. Every action taken by the driver (throttle, brakes, pantographs, etc) as well as signalling aspects (for AVK-2, and conventional signals (via the ATS and HBK signals) are recorded on magnetic tape for later analysis using a desktop computer.

Another system, known as FK, oversees the driver's alertness. The FK system is located in the brake handle. The handle itself is a button, and when the handle is pressed down, the train can operate. The FK system asks the driver to release and depress the brake handle every 60 seconds if there has been no input to the train's controls. The timer resets every time there is an action. If the handle is released, there is a grace period of about 15 seconds before an alarm sounds. If the alarm sounds for 10 seconds, the emergency brakes are applied.

A small amount of overspeed allowance is allowed before the AVK system will activate the emergency brakes. For 30 km/h the tolerance is 2 km/h. Below 80 km/h, the tolerance is 5 km/h. Between 80 km/h and 160 km/h it is 10 km/h. At speeds in excess of 160 km/h, it is 15 km/h. If the speed is in the tolerance speed, an overspeed warning buzzer sounds, and is not deactivated until the speed goes below the limit speed again. If the speed exceeds the safety tolerance the buzzer switches to an alarm and the brakes apply to bring the speed within the tolerance. If the driver does not aknowledge the alarm and safety braking after 5 seconds of braking, the emergency brakes will activate and the train will be stopped. The alarm does not switch off until the train comes to a complete stop.

Cab Display

In the centre of the driver's desk in an HHT cab, or on any other AVK-equipped train, just below the windscreen, there is the speedometer. The permitted speed is showed in a bar over the actual speed, as well as on a numerical readout next to the speedometer. As the braking curve is enforced, the speed limit bar decreases in real time, allowing the driver to adjust his braking rate accordingly. All the in-cab signalling displays must be very reliable, since they are critical to safety. The coded software is safety-critical, and enforces that the current aspect being displayed to the driver is correct. If there is a failure in the display unit, appropriate action is taken to stop the train.

The speedometer abouard an N700A HHT train is visible on leftmost digital screen. The AVK readout is 30 km/h.

AVK-2 has extensive redundancy built into it, and one might wonder why it is not used to control the train directly. However, keeping in mind the lack of adaptability of the system to unexpected situations, it is considered desirable to retain a human in the loop. Driving an HHT is therefore done entirely manually, but the signalling system keeps a very close watch to ensure maximum safety.

Conventional Cab Signalling (ATB System)

A simplified diagram on how the train reads the pulse code sent by the ATB system through the forward axle of the train and a sensor.

All main rail lines in Goyanes are equipped for cab signalling using the ATB (Atomatisk TogBeinnlflytelse; Automatic Train Supervision) system, with the exception of the HHT lines (AVK is used instead). ATB was installed beginning in 1930 on the main line of the Grand Trunk Railroad after a 1925 Ministry of Railways mandate that required automatic train protection systems after a fatal accident in Madelein, Osanhalt in 1921. Nasjonalsignalen and Eindrisson developed competing systems, but ultimately the Nasjonalsignalen one was used.

Operation of the ATB system is as follows: a 100 Hz (and in lines equipped for travel at or above 140 km/h a 250 Hz overlaid) AC voltage is applied to the rails. The voltage is switched on and off at various frequencies (known as the pulse code) which can be decoded by the train. The circuit of the track current loop is closed by the leading axle of the train, causing a magnetic field to be created around the rails. Two coils mounted ahead of the axle, usually behind the snowplow, pick up the magnetic fields, converting them into electrical signals read by the ATB equipment onboard.

An integrated ATB-Speedometer aboard a train. The current readout is a maximum speed of 80 km/h.

Overspeeding is permitted within 5 km/h of the set speed. When this happens, an overspeed light turns on. If a train accelerates faster than 5 km/h above the ATB-set limit (doesn’t apply when braking to a new lower speed limit), an alarm will sound, and the overspeed light will begin to blink. If the driver does not commence braking within 3 seconds of the alarm starting, ATB will engage the emergency brakes and cut traction power. Once the train has stopped completely, the ATB system can be unlocked, the alarm will shut off, and the train can proceed again.

When a speed limit change occurs a chime sounds. When the speed limit is lowered, and the train is travelling faster than the new limit, the driver must begin braking within 5 seconds. If not, the ATB system will begin an emergency stop. If the braking rate is not sufficient an chime will sound, and a light labeled “Brake Demand” will turn on, indicating the driver must brake harder. If more braking is not applied in 5 seconds, once again, the emergency brake and associated alarm will activate, and the “brake demand” light will blink. The alarm will silence once the train is within the mandated braking rate.

The sensor that reads the ATB pulse codes as they go through the front axle of the train.

Once the train has slowed to the new speed limit, the Limit Reached Chime will sound twice, and the “limit reached” light will momentarily turn on, indicating that the train is now locked into the lower limit and that the normal overspeed protection is active again.

The signal system is split into blocks, however each block is usually split into at least two ATB circuits. This allows ATB to allow drivers to slow down before a caution signal (which enforces a 40 km/h speed limit), for example. In addition, having multiple circuits per block allows speed limits defined by track geometry (i.e. curves) to be announced ahead of time so drivers can slow down. Because the ATB system uses continuous transmission of information, when a signal ahead clears up resulting in a speed limit raise, the driver is instantly notified (unlike AVK which transmits information at periodic intervals when the train passes over a transponder). This allows for closer train headways and higher punctuality.

The premise is that the ATB system will inform the driver of (as well as enforce) the maximum speed along that section of track, and the traditional signal system will inform the driver of the status of the track ahead. ATB is linked to and controlled by the signal system, so ATB will automatically create slowdown buffers in front of restrictive signals as well as clear up as signals clear. ATB does not waive the driver from his responsibility to be paying attention to signals, ATB simply makes the signal system more comprehensive and efficient.

ATB can also prevent starting against orders of a red signal. When the 0 ppm code is given, this translates to a 0 km/h speed limit, therefore ordering the train to stop before the signal mast. If the train tries to pass the signal while it is still red, they will not be allowed to increase past 5 km/h without activating the emergency brake. If a signaller has opened the shunting signal to allow trains to be coupled, a 25 ppm code will be sent through the tracks, allowing a 30 km/h speed limit to be used for shunting operations.

The 147 ppm code is known as the standby code. When a train exits an ATB-protected area, the train passes over a short section with 147 ppm code that automatically places the unit onto a standby mode. The system will essentially be offline until it detects a 147 ppm code (or any pulse code for that matter) upon entering a new track area, at which point it will automatically activate again. The ATB onboard computer can be manually brought in and out of standby mode as well.

Here is a guide to the various speed codes used by ATB:

100 Hz Code	250 Hz Code	Cab Signal Speed
0	--	0 km/h
25	--	30 km/h
50	--	40 km/h
75	--	60 km/h
96	--	80 km/h
120	--	90 km/h
147	--	Standby Code
180	--	100 km/h
220	--	120 km/h
270	--	130 km/h
420	--	140 km/h
270	270	150 km/h
420	420	160 km/h

Automatic Train Stop (ATS-V)

A legacy transponder from the original series of installations. The wooden ramps are to protect the transponder from flying debris that falls off trains.

ATS-V (Automatisk TogStanna-Vægr; Automatic Train Stop-Transponder) is a transponder-based train protection system that was invented in 1970 and installed nationwide beginning in 1972 after a deadly 1967 accident in Heidekerby, Nyhett during a blizzard in which an engineer passed a signal at danger since he did not see the signal, resulting in the train crashing head on with a train stopped in the station. The system not only prevents running a signal at danger, but also serves to stop the train ahead of a red signal if it is going too fast to stop, and to require confirmation from the driver when passing a yellow or double yellow signal. Previously, some lines used automatic train stop systems that relied on track-mounted tripcocks and train-mounted anglecocks, and continue to be used on certain railways, such as the Gojannesstad U-Baner.

ATS-V makes use of inductive coupling between a transceiver mounted on the train and a passive transponder mounted on the track that oscillates at preset frequencies when activated by the magnetic field from the aforementioned transceiver. The transponders require no outside power, however there is a cable that is connected to the signal equipment to control small relays inside the transponder which switch capacitors in/out of the coil circuit and determine which frequency is detected by the passing train.

A newer style transponder. They are more flushly mounted with the track to avoid the use of wooden protective ramps. The transponders are also more powerful, preventing malfunctions and bad reads when snowfall is present.

Each transponder is offset from the centerline of the track as they are directional. The transponders are mounted at 5 meters before the signal and at 300 meters before the signal (less if the block is short). The 5-meter transponder serves the signal confirmation function and the signal passing at danger function. When a train passes the 5-meter transponder and the signal is yellow or double yellow it will sound a chime and turn on a light, requesting a confirmation button press. If the button is not pressed within 3 seconds of the chime the emergency brakes will be applied and the alarm will activate. If the signal is red, passing the 5-meter transponder will automatically trigger the emergency brakes. Passing the 5-meter transponder with a green-yellow, green, or double green aspect will a small green “ATS OK” light to momentarily switch on.

Even though ATB limits the speed of trains within blocks with yellow signals, when trains run on lines without ATB or if ATB malfunctions a train could potentially run up on a red signal with excess speed, unable to stop short of the signal. To fix this, (usually) 300 meters before the signal there are a pair of ATS-V transponders spaced .5 meters apart. When the train passes over the first transponder a speed check is initiated. The onboard component of ATS-V is programmed with the time it should take between transponders at 60 km/h. If the time is too short between transponders (meaning the speed is more than 60 km/h), the emergency brakes will be applied in order to bring the train to a halt before the signal is passed at danger (or if it is passed, the train will not stray as far into the next block). If the second transponder is not detected in 5 seconds, the speed is assumed to be permissible.

If the train is stopped due to overspeed before a red signal, an “Overspeed ATS” light will turn on and an alarm will activate, which will not shut off until the ATS-V system is unlocked once the train comes to a stop.

The frequencies and their meanings are as follows: 60 kHz - Proceed; 64 kHz - Initiate speed timer; 68.3 kHz - End speed timer and calculate; 88.5 kHz - Confirm cautionary signal; 95.5 kHz - Stop; 99.3 kHz - Error.

Here is a guide to the oscillation frequencies used by ATS-V:

Oscillation Frequency	Meaning
60 kHz	Proceed
64 kHz	Initiate Speed Check
68.3 kHz	End Speed Check, Start Calculation
88.5 kHz	Confirm Cautionary Signal
95.5 kHz	Stop
99.3 kHz	Error

Signage

Sign	Meaning
	Speed Limit; displayed in multiples of 10. In this case, 120 km/h.
	Junction Speed Limit; applies in the diverging route or track indicated.
	Advance Warning of Speed Limit; warns of a lower speed limit ahead, displayed in multiples of 10. In this case, 80 km/h.
	Advance Warning of Junction Speed Limit; warns of a lower speed limit ahead on a specified track, displayed in multiples of 10. In this case, 80 km/h.
	Advance Warning of a Temporary Emergency Speed Limit; displayed in multiples of 10. In this case, 30 km/h.
	Temporary Emergency Speed Limit; applies to all trains.
	End Temporary Emergency Speed Limit; applies to all trains.
	Raise Pantograph; The train must raise the pantograph and retract contact shoes.
	Lower Pantograph; The train must lower the pantograph and deploy contact shoes.
	Do Not Raise Pantograph; Despite the presence of overhead lines, do not raise the pantographs.
	Change In Current; The exact point where the change in current collection happens.
	Neutral Zone Advance Warning; There is a neutral zone in specified distance (meters).
	Long Neutral Zone Warning; The neutral zone ahead is of considerable length.
	Open Breakers; By this point circuit breakers must be open.
	Close Breakers; By this point circuit breakers must be closed.
	Current Indicator; Indicates the current type being used.
	End Current; The current of the specified type is ending.
	Whistle Board; The train must sound its horn or whistle when passing the sign.
	Close Air Vents; Reminder to the driver that a tunnel is approaching and they must close the air vents to avoid a pressure difference.
	Train All Stop; All trains, regardless of length or type, must stop at this sign.
	HHT Train Stop; HHT Trains must stop at the sign. The number indicates the number of trainsets that it applies to.
	Train Type Stop; Trains of the specified type(s) must stop at the sign.
	Train Car Stop; Trains of the car quantity specified must stop at the sign.
	AVK Begin; The track ahead is equipped with AVK, the system should exit standby mode.
	End AVK; The track ahead is no longer equipped with AVK, drivers are instructed to set the AVK to standby mode.
	Override ATS; The ATS transmitter is not aligned for the operating direction. Drivers have permission to override the signal.