BART's Train Control System
The following page contains only publicly-released details on BART's Automatic Train Control system.
Amazingly, early BART and Westinghouse were proud to explain how their Train Control System operates - in turn, showing off how BART was the most advanced and safest railroad ever built, at the time. Naturally, this information is geared towards the historical side and captures what those early BARTonians thought was interesting to the future riders of BART.
This article was written under the assumption that conditions are nearly perfect. Naturally, procedures change and varying degrees of manual control occur on a daily basis.
Amazingly, early BART and Westinghouse were proud to explain how their Train Control System operates - in turn, showing off how BART was the most advanced and safest railroad ever built, at the time. Naturally, this information is geared towards the historical side and captures what those early BARTonians thought was interesting to the future riders of BART.
This article was written under the assumption that conditions are nearly perfect. Naturally, procedures change and varying degrees of manual control occur on a daily basis.
BART's train control system is a marvel in action - it's another piece of technology that keeps BART rolling, and even 50 years into service, it's still a rather advanced and reliable method of train control. BART's Train Control system pioneered the development of other train control systems across the world. This page is a basic overview of the system as it was in the 1970s.
Central Computer and Central Control
Central and the old "big board"
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The central computer and its associated system supervises the operation of the BART system - it was the first system in the world to have automatic train supervision. The computer "optimizes" the system in modifying train performance to match the schedule and making "suggestions" on ways to cope with unexpected situations. Naturally, the computer cannot override safety. Controllers at central also provide ways to respond to situations beyond the capacity of the computer.
The central computer's system also controls destination signs on the platform. |
The old central computer
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Automatic Train Control System (ATC)
The page deals with the original "legacy" automatic train control system, installed in the original portions of the BART system (Fremont-Concord-Richmond-Daly City), with exceptions. The extensions use newer technology.
The ATC system consists of the following subsystems:
Multiplex and Speed Encoding (MUX)
Interlocking System
Automatic Train Operation (ATO)
A back up system (Manual Block/CABS II/CABS I/SORS)
The ATC system consists of the following subsystems:
Multiplex and Speed Encoding (MUX)
Interlocking System
Automatic Train Operation (ATO)
A back up system (Manual Block/CABS II/CABS I/SORS)
Multiplex and Speed Encoding (MUX)
The multiplex/speed encoding system (MUX) detects trains, and generates and transmits speed codes (aka speed commands) to trains. There are eight possible speed commands: 0, 6, 18, 27, 36, 50, 70, or 80 mph.
Tracks are divided into segments (track circuits, which include both running rails and shunts).
Tracks are divided into segments (track circuits, which include both running rails and shunts).
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Interlocking System
The interlocking system ensures the alignment of switches and the safe movement of train through interlockings.
Like every other railroad in the world, switches allow for trains to change tracks (e.g. from track 1 to track 2).
Like every other railroad in the world, switches allow for trains to change tracks (e.g. from track 1 to track 2).
Automatic Train Operation (ATO)
ATO is the system that stops trains at stations, commands the opening and closing of doors, regulates how long the train remains in the station (dwell time), requests routes, and transmits performance levels.
A pair of wires are laid out on the wayside in a fashion that allows the train to receive a signal, bringing the train to a stop at the proper position on a station platform. The train itself calculates the proper position, and applies braking to stop smoothly in the station.
The doors open automatically, and the train operator receives a chime notifying them to close the doors. The train departs the station, and reaches the maximum speed generated by MUX but modified by ATO (the performance level).
Performance level 2 is the default performance level, and the only noticeable difference from full performance is that trains run at 70 mph while MUX generates an 80 mph code. During wet and hot conditions, central can reduce every trains' performance level, in turn reducing speeds.
A pair of wires are laid out on the wayside in a fashion that allows the train to receive a signal, bringing the train to a stop at the proper position on a station platform. The train itself calculates the proper position, and applies braking to stop smoothly in the station.
The doors open automatically, and the train operator receives a chime notifying them to close the doors. The train departs the station, and reaches the maximum speed generated by MUX but modified by ATO (the performance level).
Performance level 2 is the default performance level, and the only noticeable difference from full performance is that trains run at 70 mph while MUX generates an 80 mph code. During wet and hot conditions, central can reduce every trains' performance level, in turn reducing speeds.
A back up system (Manual Block/CABS II/CABS I/SORS)
In summer 1972, train detection tests revealed a failure with potentially catastrophic results - ATC as it stood was not 100% reliable in train detection, and could actually fail to detect dead cars on various blocks.
Manual Block
As required by the CA Public Utilities Commission, BART added a back up plan - manual block procedure, which supervisors placed at every other station would phone ahead to ensure the track was clear for the train at their station. This ensured two station separation between trains at all times. BART's opening day was under this procedure, as was the extension to Richmond (1/29/1973); the opening of the Concord line (Concord to MacArthur (5/21/1973); and Montgomery Street to Daly City (11/5/1973).
CABS II
By 1973, BART forces were able to use the central computer to replicate the two station seperation. This procedure, called CABS II (Computer Automated Block System, Two Station Separation) began operating on the Concord line on October 19, 1973, and replaced the manual block system on the Concord line on February 20, 1974. The Fremont - Richmond line followed on April 23, 1974, alongside the San Francisco "Intra-City Line" on May 21, 1974.
CABS I
CABS I, standing for Computer Automated Block System, One Station Separation, was the advancement of CABS II for only one station of separation. As an extra measure of safety, CABS I included the installation of a zero-speed gate (aka trap) past every station to prevent the possibility of run-throughs (no stop) or inadvertent train releases. CPUC approved CABS I for the Richmond-Fremont line on July 2, 1974; Concord line on July 11, 1974, and San Francisco "Intra City Line" on July 16, 1974. The Transbay Tube also received a modification - a pseudo station under the Bay named M00 ("Moo") which ensured one station separation given the distance between Embarcadero and Oakland West stations. CPUC required five corrective measures to the system (based on service reliability and not safety), and the Tube opened to revenue riders in September 1974 under CABS I.
SORS (Sequential Occupancy Release System)
SORS (originally called SOR) acts as a latest back-up to train detection, originally installed in 1974. It's a computer system that prevents rear-end collisions by latching on to the track behind the front of a train, and releases the section of track once the train has completely exited said section. SORS replaced CABS I, and does not require any station separation.
Manual Block
As required by the CA Public Utilities Commission, BART added a back up plan - manual block procedure, which supervisors placed at every other station would phone ahead to ensure the track was clear for the train at their station. This ensured two station separation between trains at all times. BART's opening day was under this procedure, as was the extension to Richmond (1/29/1973); the opening of the Concord line (Concord to MacArthur (5/21/1973); and Montgomery Street to Daly City (11/5/1973).
CABS II
By 1973, BART forces were able to use the central computer to replicate the two station seperation. This procedure, called CABS II (Computer Automated Block System, Two Station Separation) began operating on the Concord line on October 19, 1973, and replaced the manual block system on the Concord line on February 20, 1974. The Fremont - Richmond line followed on April 23, 1974, alongside the San Francisco "Intra-City Line" on May 21, 1974.
CABS I
CABS I, standing for Computer Automated Block System, One Station Separation, was the advancement of CABS II for only one station of separation. As an extra measure of safety, CABS I included the installation of a zero-speed gate (aka trap) past every station to prevent the possibility of run-throughs (no stop) or inadvertent train releases. CPUC approved CABS I for the Richmond-Fremont line on July 2, 1974; Concord line on July 11, 1974, and San Francisco "Intra City Line" on July 16, 1974. The Transbay Tube also received a modification - a pseudo station under the Bay named M00 ("Moo") which ensured one station separation given the distance between Embarcadero and Oakland West stations. CPUC required five corrective measures to the system (based on service reliability and not safety), and the Tube opened to revenue riders in September 1974 under CABS I.
SORS (Sequential Occupancy Release System)
SORS (originally called SOR) acts as a latest back-up to train detection, originally installed in 1974. It's a computer system that prevents rear-end collisions by latching on to the track behind the front of a train, and releases the section of track once the train has completely exited said section. SORS replaced CABS I, and does not require any station separation.
Sources:
BART 50th anniversary scanned documents
BART Background Information: CABS Story (SHORT HISTORY OF THE COMPUTER AUTOMATED BLOCK SYSTEM)
Westinghouse Press Releases
News articles from the 1960s through 1970s
BART 50th anniversary scanned documents
BART Background Information: CABS Story (SHORT HISTORY OF THE COMPUTER AUTOMATED BLOCK SYSTEM)
Westinghouse Press Releases
News articles from the 1960s through 1970s
