ACSES
Encyclopedia
Advanced Civil Speed Enforcement System (ACSES) is a positive train control
cab signaling
system developed by PHW and Alstom
. The system is designed to prevent train
-to-train collisions
, protect against overspeed and protect work crews with temporary speed restrictions. The information about permanent and temporary speed restrictions is transmitted to the train by transponder
s lying in the track, coded track circuit
s and digital radio
. It is installed on Amtrak
's Northeast Corridor
between Washington
and Boston.
s to improve safety by mitigating against human error
. It applies train brake systems depending on the information about speed restrictions transmitted to the train.
There are two kinds of speed restrictions, which are enforced by the system:
In the event a train's crew exceed a speed restriction the train's brake systems are applied to reduce the speed to comply with the restrictions. In the event that braking is ordered by the onboard computer system, event recording is performed that records the fact that braking was required so that railroad managers can determine whether additional training is needed for their onboard locomotive crews.
Speed restrictions required by the signal system
are provided by the legacy pulse code cab signals
system, which has been in service on various railroads since the 1930s. The cab signal codes are fed into the ACSES cab display unit, which then enforces the more restrictive of the two speeds. The on board ACSES unit is backwards compatible and can function where only the cab signaling is present without the ACSES overlay.
In addition to ensuring maximum safe speed, the system also ensures maximum return on investment by safely authorizing a locomotive’s maximum speed. Locomotives need not come to a halt while onboard crew communicate with their dispatch controllers via radio to determine whether speed restrictions are in effect or whether maintenance crew are in possible harm’s way. Locomotives know in advance of any such restrictions, allowing them to proceed at best safe speed without interruptions.
(AREMA) organization describes what it means by Positive Train Control
and among the most salient aspects are:
The PHW and Alstom ACSES systems meets these core requirements.
subsystem, and a radio
subsystem. In the cab, the driver has a consolidated display which displays the train's target speed and other useful operating information.
Messages conveyed to and from locomotive and ground-based systems are made up of ATCS-encoded (Advanced Train Control Systems) message frames.
when a locomotive passes over them. The transponders digitally convey their identification information and other relevant bits of information via wires to a trackside Safetran
Base Station Controller (BCM), which uses a Safetran radio to communicate with the locomotive’s onboard computers, allowing the locomotives to know precisely when they have reached a particular waypoint
along the track.
The onboard systems examine its database of speed restrictions, constantly ensuring that the maximum safe speed for any given location along the track is not exceeded.
As the locomotive proceeds down the track, the onboard systems communicate via radio to the trackside BCMs in the region, requesting any temporary speed restrictions for the next three or more regions of the track, ensuring that the locomotive’s database is always kept current with any possible temporary restrictions issued by the dispatch and control office equipment.
Also in the field are Safetran Wayside Communications Managers (WCM) (or packet switch
es), which communicate with BCMs in the region via radio which also communicate with the office dispatch and control systems via TCP/IP.
This design provides locomotives with positive information about where they are and what their maximum safe speeds are, and it also keeps the office informed about where the locomotives are located.
In addition to speed restrictions, information about the tracks ahead can be acquired by the ground network which informs locomotives of the state and status of the tracks which the locomotive are approaching. Such information about the status of the track ahead—occupancy, switch position, signal light states, and a host of other vital inputs—is accumulated by wayside encoders such as the Safetran VIU-ACSES (shown in the photograph to the right) and then the information is sent to the BCMs for transmission
to locomotives.
where dispatch and control is performed, a system provides a visual indication of the current status of communications with all locomotives as well as a close approximation
of where each locomotive is currently located along the track.
In the event that maintenance is needed along any section of the track, before a work crew is dispatched or before a work crew is granted authority to proceed, a temporary speed restriction (TSR) is created in the office computer systems. After a series of verifications and procedures, the TSR is presented to the ACSES office system.
When a locomotive issues a query for TSRs for a given region, the WCM conveys the request for information to the office system via TCP/IP and the response is conveyed back to the locomotive which updates its local database with any restrictions.
or lightning strike
results in a standby WCM taking over the communications duties between BCMs and the office systems.
In the event of a loss of all redundant standby systems (such as might occur in a catastrophic environmental condition as might be expected with a hurricane or forest fire) the entire system immediately drops to its failsafe states.
Because a locomotive's radio is capable of being heard by a number of BCMs, the WCM examines the indication RF signal strength of each BCM that heard the locomotive to determine what the strongest talk path back to the locomotive is. The WCM maintains a record of three possible talk paths to the locomotive such that the strongest path is always selected if the office needs to communicate back to the locomotive.
As a locomotive moves from region to region, the radio signal strengths recorded by BCMs which get conveyed to the WCMs change. BCMs which fall out of range of locomotives are removed from talk path routes within the WCM in favor of the BCMs which are coming in to range.
In this way the WCM is constantly aware of where each locomotive is located and which talk path is best used to communicate with the locomotive. Such information is also conveyed to the office so that office systems may make use of it.
Another aspect of redundancy is the system design which looks forward along the track, acquiring TSRs for the future in the event a temporary communications failure occurs. Since each locomotive has TSRs for at least three future segments of the rail line, in the event there is a segment of the track which for some reason has lost radio communication to the office, the locomotive has TSR information for the "dark" segment already before it proceeds in to the dark segment.
Finally, the cab signals are considered a completely independent system that transmits a continuous stream of codes through the rails instead of via wireless transmission. Any fault in the ACSES overlay will not affect the cab signal system.
With Positive Train Control in effect, a series of authorization steps are needed to convince the onboard computer systems to allow the locomotive to proceed at maximum safe speed after the onboard crew acquire such authorization from the dispatch and control center—usually via radio.
Positive Train Control
Positive train control is a system of monitoring and controlling train movements to provide increased safety.-Overview:The main concept in PTC is that the train receives information about its location and where it is allowed to safely travel, also known as movement authorities...
cab signaling
Cab signalling
Cab signalling is a railway safety system that communicates track status information to the cab, crew compartment or driver's compartment of a locomotive, railcar or multiple unit, where the train driver or engine driver can see the information....
system developed by PHW and Alstom
Alstom
Alstom is a large multinational conglomerate which holds interests in the power generation and transport markets. According to the company website, in the years 2010-2011 Alstom had annual sales of over €20.9 billion, and employed more than 85,000 people in 70 countries. Alstom's headquarters are...
. The system is designed to prevent train
Train
A train is a connected series of vehicles for rail transport that move along a track to transport cargo or passengers from one place to another place. The track usually consists of two rails, but might also be a monorail or maglev guideway.Propulsion for the train is provided by a separate...
-to-train collisions
Train wreck
A train wreck or train crash is a type of disaster involving one or more trains. Train wrecks often occur as a result of miscommunication, as when a moving train meets another train on the same track; or an accident, such as when a train wheel jumps off a track in a derailment; or when a boiler...
, protect against overspeed and protect work crews with temporary speed restrictions. The information about permanent and temporary speed restrictions is transmitted to the train by transponder
Transponder
In telecommunication, the term transponder has the following meanings:...
s lying in the track, coded track circuit
Track circuit
A track circuit is a simple electrical device used to detect the absence of a train on rail tracks, used to inform signallers and control relevant signals.- Principles and operation :...
s and digital radio
Digital radio
Digital radio has several meanings:1. Today the most common meaning is digital radio broadcasting technologies, such as the digital audio broadcasting system, also known as Eureka 147. In these systems, the analog audio signal is digitized into zeros and ones, compressed using formats such as...
. It is installed on Amtrak
Amtrak
The National Railroad Passenger Corporation, doing business as Amtrak , is a government-owned corporation that was organized on May 1, 1971, to provide intercity passenger train service in the United States. "Amtrak" is a portmanteau of the words "America" and "track". It is headquartered at Union...
's Northeast Corridor
Northeast Corridor
The Northeast Corridor is a fully electrified railway line owned primarily by Amtrak serving the Northeast megalopolis of the United States from Boston in the north, via New York to Washington, D.C. in the south, with branches serving other cities...
between Washington
Washington, D.C.
Washington, D.C., formally the District of Columbia and commonly referred to as Washington, "the District", or simply D.C., is the capital of the United States. On July 16, 1790, the United States Congress approved the creation of a permanent national capital as permitted by the U.S. Constitution....
and Boston.
General system design
ACSES enforce speed restrictions upon trainTrain
A train is a connected series of vehicles for rail transport that move along a track to transport cargo or passengers from one place to another place. The track usually consists of two rails, but might also be a monorail or maglev guideway.Propulsion for the train is provided by a separate...
s to improve safety by mitigating against human error
Human Error
Human Error is the stage name of Rafał Kuczynski , a polish electronic musician, working mostly in the ambient music genre, produced only with a computer...
. It applies train brake systems depending on the information about speed restrictions transmitted to the train.
There are two kinds of speed restrictions, which are enforced by the system:
- Permanent Speed Restrictions are applied to trains to ensure that the maximum safe speed for track conditions and other environmental factors are not exceeded. These speed restrictions are also called civil speed restrictions.
- Temporary speed restrictions are applied to trains in the event of maintenance crews working on wayside equipment along the tracks to improve worker safety.
In the event a train's crew exceed a speed restriction the train's brake systems are applied to reduce the speed to comply with the restrictions. In the event that braking is ordered by the onboard computer system, event recording is performed that records the fact that braking was required so that railroad managers can determine whether additional training is needed for their onboard locomotive crews.
Speed restrictions required by the signal system
North American railway signaling
Standards for North American railway signaling in the United States are issued by the Association of American Railroads , which is a trade association of the railroads of Canada, the USA, and Mexico. Their system is loosely based on practices developed in the United Kingdom during the early years...
are provided by the legacy pulse code cab signals
Pulse code cab signaling
Pulse code cab signaling is a form of cab signaling developed in the United States by the Union Switch and Signal corporation for the Pennsylvania Railroad in the 1920s...
system, which has been in service on various railroads since the 1930s. The cab signal codes are fed into the ACSES cab display unit, which then enforces the more restrictive of the two speeds. The on board ACSES unit is backwards compatible and can function where only the cab signaling is present without the ACSES overlay.
In addition to ensuring maximum safe speed, the system also ensures maximum return on investment by safely authorizing a locomotive’s maximum speed. Locomotives need not come to a halt while onboard crew communicate with their dispatch controllers via radio to determine whether speed restrictions are in effect or whether maintenance crew are in possible harm’s way. Locomotives know in advance of any such restrictions, allowing them to proceed at best safe speed without interruptions.
ACSES meets definition of Positive Train Control
The American Railway Engineering and Maintenance-of-Way AssociationAmerican Railway Engineering and Maintenance-of-Way Association
The American Railway Engineering and Maintenance-of-Way Association is a North American railway industry group. It publishes recommended practices for the design, construction and maintenance of railway infrastructure, which are requirements in the United States and Canada.-Overview:AREMA is...
(AREMA) organization describes what it means by Positive Train Control
Positive Train Control
Positive train control is a system of monitoring and controlling train movements to provide increased safety.-Overview:The main concept in PTC is that the train receives information about its location and where it is allowed to safely travel, also known as movement authorities...
and among the most salient aspects are:
- Train separation (collision avoidance)
- Civil speed restrictions enforcement
- Temporary speed restrictions
- Rail worker wayside safety
The PHW and Alstom ACSES systems meets these core requirements.
On-board equipment
The on-board equipment consists of an on-board computer, an antennaAntenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
subsystem, and a radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
subsystem. In the cab, the driver has a consolidated display which displays the train's target speed and other useful operating information.
Messages conveyed to and from locomotive and ground-based systems are made up of ATCS-encoded (Advanced Train Control Systems) message frames.
Field equipment
The system begins with passive transponders buried under the tracks which are electrically powered by an electromagnetic fieldElectromagnetic field
An electromagnetic field is a physical field produced by moving electrically charged objects. It affects the behavior of charged objects in the vicinity of the field. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction...
when a locomotive passes over them. The transponders digitally convey their identification information and other relevant bits of information via wires to a trackside Safetran
Safetran
Safetran Systems Corporation is a US-based supplier of switch machines, railroad wayside signal systems, rail transit signaling and rail-highway grade crossing active warning systems....
Base Station Controller (BCM), which uses a Safetran radio to communicate with the locomotive’s onboard computers, allowing the locomotives to know precisely when they have reached a particular waypoint
Waypoint
A waypoint is a reference point in physical space used for purposes of navigation.-Concept:Waypoints are sets of coordinates that identify a point in physical space. Coordinates used can vary depending on the application. For terrestrial navigation these coordinates can include longitude and...
along the track.
The onboard systems examine its database of speed restrictions, constantly ensuring that the maximum safe speed for any given location along the track is not exceeded.
As the locomotive proceeds down the track, the onboard systems communicate via radio to the trackside BCMs in the region, requesting any temporary speed restrictions for the next three or more regions of the track, ensuring that the locomotive’s database is always kept current with any possible temporary restrictions issued by the dispatch and control office equipment.
Also in the field are Safetran Wayside Communications Managers (WCM) (or packet switch
Packet switch
A packet switch is a node in a network which uses the packet switching paradigm for data communication. Packet switches can operate at a number of different levels in a protocol suite; although the exact technical details differ, fundamentally they all perform the same function: they store and...
es), which communicate with BCMs in the region via radio which also communicate with the office dispatch and control systems via TCP/IP.
This design provides locomotives with positive information about where they are and what their maximum safe speeds are, and it also keeps the office informed about where the locomotives are located.
In addition to speed restrictions, information about the tracks ahead can be acquired by the ground network which informs locomotives of the state and status of the tracks which the locomotive are approaching. Such information about the status of the track ahead—occupancy, switch position, signal light states, and a host of other vital inputs—is accumulated by wayside encoders such as the Safetran VIU-ACSES (shown in the photograph to the right) and then the information is sent to the BCMs for transmission
Transmission (telecommunications)
Transmission, in telecommunications, is the process of sending, propagating and receiving an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium, either wired, optical fiber or wireless...
to locomotives.
Office equipment
In the officeOffice
An office is generally a room or other area in which people work, but may also denote a position within an organization with specific duties attached to it ; the latter is in fact an earlier usage, office as place originally referring to the location of one's duty. When used as an adjective, the...
where dispatch and control is performed, a system provides a visual indication of the current status of communications with all locomotives as well as a close approximation
Approximation
An approximation is a representation of something that is not exact, but still close enough to be useful. Although approximation is most often applied to numbers, it is also frequently applied to such things as mathematical functions, shapes, and physical laws.Approximations may be used because...
of where each locomotive is currently located along the track.
In the event that maintenance is needed along any section of the track, before a work crew is dispatched or before a work crew is granted authority to proceed, a temporary speed restriction (TSR) is created in the office computer systems. After a series of verifications and procedures, the TSR is presented to the ACSES office system.
When a locomotive issues a query for TSRs for a given region, the WCM conveys the request for information to the office system via TCP/IP and the response is conveyed back to the locomotive which updates its local database with any restrictions.
Redundancy
There are a number of redundant components in the overall ACSES system such that a failure of a subsystem will swap over to another automatically. The loss of a WCM, for example, due to a power outagePower outage
A power outage is a short- or long-term loss of the electric power to an area.There are many causes of power failures in an electricity network...
or lightning strike
Lightning strike
Lightning strikes are electrical discharges caused by lightning, typically during thunderstorms.Humans can be hit by lightning directly when outdoors. Contrary to popular notion, there is no 'safe' location outdoors. People have been struck in sheds and makeshift shelters...
results in a standby WCM taking over the communications duties between BCMs and the office systems.
In the event of a loss of all redundant standby systems (such as might occur in a catastrophic environmental condition as might be expected with a hurricane or forest fire) the entire system immediately drops to its failsafe states.
Because a locomotive's radio is capable of being heard by a number of BCMs, the WCM examines the indication RF signal strength of each BCM that heard the locomotive to determine what the strongest talk path back to the locomotive is. The WCM maintains a record of three possible talk paths to the locomotive such that the strongest path is always selected if the office needs to communicate back to the locomotive.
As a locomotive moves from region to region, the radio signal strengths recorded by BCMs which get conveyed to the WCMs change. BCMs which fall out of range of locomotives are removed from talk path routes within the WCM in favor of the BCMs which are coming in to range.
In this way the WCM is constantly aware of where each locomotive is located and which talk path is best used to communicate with the locomotive. Such information is also conveyed to the office so that office systems may make use of it.
Another aspect of redundancy is the system design which looks forward along the track, acquiring TSRs for the future in the event a temporary communications failure occurs. Since each locomotive has TSRs for at least three future segments of the rail line, in the event there is a segment of the track which for some reason has lost radio communication to the office, the locomotive has TSR information for the "dark" segment already before it proceeds in to the dark segment.
Finally, the cab signals are considered a completely independent system that transmits a continuous stream of codes through the rails instead of via wireless transmission. Any fault in the ACSES overlay will not affect the cab signal system.
Failsafe operation
In the event that a locomotive is unable to automatically retrieve temporary speed restriction information from its office control system despite repeated retries and standby backup systems, the failsafe fallback policies established for the railroad are adopted and traditionally the locomotives reduce speed and require a human operator to communicate with a dispatch center for authority to proceed.With Positive Train Control in effect, a series of authorization steps are needed to convince the onboard computer systems to allow the locomotive to proceed at maximum safe speed after the onboard crew acquire such authorization from the dispatch and control center—usually via radio.