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From page 8... ... SECTION 5 8 Secondary Train Detection/Protection Systems In the context of CBTC, a secondary train detection/protection system (STD/PS) is a signaling system comprised of, but not limited to: • A secondary train detection system only, or • Both secondary train detection and secondary train protection systems. Read the entire page →
From page 9... ... SECTION 5 – SECONDARY TRAIN DETECTION/PROTECTION SYSTEMS 9 train control system using onboard electronics and train‐wayside communications such as coded track circuits. So far, there have been very few projects in the world where a CBTC system was replaced by another, but it is expected to be more frequent as the first CBTC systems reach their end of life. Due to problems such as space on board the trains, obsolescence, and availability of onboard electronic equipment, the secondary systems considered in CBTC projects are conventional signaling systems and not cab signaling or other type of ATC. 5.1 Detection Systems 5.1.1 Track Circuits Regardless of the technology used to implement safety principles of STD/PS, the foundation of STD/PS is train detection, and traditionally this has been the track circuit. The Association of American Railroads defines a track circuits as: "An electrical circuit of which the rails of the track form a part." A track circuit is a section of track with a source of energy connected across the running rails at one end of the track section (the "feed" end) and a device that is operated by this energy at the other end of the track section. The device has traditionally been an electromechanical relay, so this end of the track circuit is called the "relay" end. Under normal conditions, there is no train or other vehicle occupying the track section. The energy at the feed end energizes the detection device at the relay end using the rails as conductors; the circuit is closed and the energized detection device indicates vacancy of the track circuit. When a train enters the section, its metal wheels and axles provide a low‐resistance path from rail to rail for the feed energy, greatly reducing or eliminating energy at the relay end that would be available for the detection device. The device then becomes de‐energized and indicates occupancy of the section. The track circuit status is used by the signal system to provide safe separation between trains and other safety functions. Note that under failure conditions, such as a broken wire, disconnected wire, missing feed, blown fuse, broken rail, etc., the circuit opens. The detection device de‐energizes and indicates occupancy even though there may not be a train present. This is a safe failure since it will be assumed by the signal system that there is a train occupying the section, keeping other trains a safe distance away. A track is divided into a continuous sequence of track circuits arranged end‐to‐end. Each circuit may also be referred to as a track section, or section. One or more track sections comprise a block whose entrance is governed by a signal. Track circuits are physically and electrically isolated from each other with insulated joints in one or both rails at each end. If insulated joints are in both rails, impedance bonds are needed at track circuit boundaries to allow traction (vehicle motor) Read the entire page →
From page 10... ... SECTION 5 – SECONDARY TRAIN DETECTION/PROTECTION SYSTEMS 10 • Coded: The steady energy used in the non‐coded track circuit is modulated at certain rates. The modulation rates represent wayside‐to‐train information sent from the feed end toward receiving equipment on a train for transmission of information such as speed codes in conjunction with non‐ CBTC automatic train control and onboard speed enforcement. • Audio frequency (AF) Read the entire page →
From page 11... ... SECTION 5 – SECONDARY TRAIN DETECTION/PROTECTION SYSTEMS 11 Compared to track circuits, there are few restrictions on the placement of axle counters. Track circuits use the rails as part of the circuit; axle counters do not. The rails are only used for mechanical mounting of the wheel detectors. Therefore, there is no concern for ballast leakage or rail resistance; little concern for traction current interference; no need for modifying the rail (or compromising its structural integrity) for insulated joints or to connect track wires and impedance bond cables. Since axle counters do not know the absolute state of their track section when they are powered up, there must be an initialization process which involves intervention of humans who know the state of the section. This must be done only when the section is truly clear and may require field confirmation. This may also require the first train after reset to enter and leave the track section -- while sweeping the section visually -- before accepting the axle counter state as valid. Manual intervention might also be needed in the case of a disturbed section, as might happen if the number of leaving wheels is more than the number of entering wheels since there cannot be a "negative" number of wheels left behind in the section. 5.2 Protection Functions Train detection lays the foundation for train protection. A train being detected is vitally mandatory for protection from a following train. An occupied block prevents the clearing of signals approaching the occupied block. In interlockings, detection additionally effects certain types of locking to provide route integrity, locking of movable rail in the route and under the train, and preventing release of said locking before it is safe to do so. The following summarizes some of these functions. 5.2.1 Automatic Block Signal System Between interlockings, STD/PS provides protection where each signal's control is arranged such that it will display red if a block in advance is occupied. The spacing between the red signal and the beginning of the occupied block is sufficient to provide safe braking distance if a train ignores the red and passes it at maximum speed. The signal will display yellow if the block in advance is vacant, but the next signal in advance is red. It will display green if the next signal is permissive (green or yellow) Read the entire page →
From page 12... ... SECTION 5 – SECONDARY TRAIN DETECTION/PROTECTION SYSTEMS 12 • Detector locking. Locks a switch while the track section that includes the switch is occupied. Prevents movement of the switch where such movement could cause a derailment. Release of detector locking is usually delayed to prevent premature unlocking due to momentary loss of shunt across the track circuit. Read the entire page →
From page 13... ... SECTION 5 – SECONDARY TRAIN DETECTION/PROTECTION SYSTEMS 13 capable of an off‐peak level of revenue service (Category 1.A.2) , where a reduction in service is possible during a complete CBTC failure or to manage non‐CBTC equipped trains. Category 1.B includes STD/PS designed to handle a single non‐CBTC train. There are also different subcategories based on performance desired when handling a single non‐CBTC train. The first sub‐ category allows one single train per interstation (Category 1.B.1) Read the entire page →
From page 14... ... • For tr • Secon Category • Signa • For tr • Less e • Secon Category per inters • Signa • For tr • Secon Dependin signals on 1.A.2) Read the entire page →
From page 15... ... Category between • Signa • For tr • Secon Category between • Signa • For tr • Secon Category specific h • No sig • Secon 1.B.2.1 – Sec interlockings ls at interlock ains operatin dary detectio 1.B.2.2 – Sec interlockings ls at interlock ains operatin dary detectio 1.B.3 – Secon eadway perf nals dary detectio ondary syste , with second ings g under STD/ n system pre ondary Syste , with second ings g under STD/ n system pre dary System ormance n system pre m designed t ary detectio PS, signals ar sent everyw Figure m designed ary detectio PS, signals ar sent only at Figure designed to sent everyw Figure SECTIO 15 o handle a s n method ev e usually not here 4: Category 1 to handle a s n method on e usually not interlockings 5: Category 1 handle a sin here 6: Category N 5 – SECONDAR ingle non‐CB erywhere enforced au .B.2.1 ingle non‐CB ly at interlo enforced au .B.2.2 gle non‐CBTC 1.B.3 Y TRAIN DETECTIO TC train, cap tomatically TC train, cap ckings tomatically train, witho N/PROTECTION S able of one t able of one t ut territory YSTEMS rain rain Read the entire page →
From page 16... ... SECTION 5 – SECONDARY TRAIN DETECTION/PROTECTION SYSTEMS 16 Category 2 – No STD/PS • Systems without STD/PS • No secondary detection system Switch position indicators showing the position of switches to manual drivers are usually used when no interlocking signals are present; however, they are not represented in the following figure. Figure 7: Category 2 Read the entire page →

From page 8...

... SECTION 5 8 Secondary Train Detection/Protection Systems In the context of CBTC, a secondary train detection/protection system (STD/PS) is a signaling system comprised of, but not limited to: • A secondary train detection system only, or • Both secondary train detection and secondary train protection systems.

Read the entire page →

From page 9...

... SECTION 5 – SECONDARY TRAIN DETECTION/PROTECTION SYSTEMS 9 train control system using onboard electronics and train‐wayside communications such as coded track circuits. So far, there have been very few projects in the world where a CBTC system was replaced by another, but it is expected to be more frequent as the first CBTC systems reach their end of life. Due to problems such as space on board the trains, obsolescence, and availability of onboard electronic equipment, the secondary systems considered in CBTC projects are conventional signaling systems and not cab signaling or other type of ATC. 5.1 Detection Systems 5.1.1 Track Circuits Regardless of the technology used to implement safety principles of STD/PS, the foundation of STD/PS is train detection, and traditionally this has been the track circuit. The Association of American Railroads defines a track circuits as: "An electrical circuit of which the rails of the track form a part." A track circuit is a section of track with a source of energy connected across the running rails at one end of the track section (the "feed" end) and a device that is operated by this energy at the other end of the track section. The device has traditionally been an electromechanical relay, so this end of the track circuit is called the "relay" end. Under normal conditions, there is no train or other vehicle occupying the track section. The energy at the feed end energizes the detection device at the relay end using the rails as conductors; the circuit is closed and the energized detection device indicates vacancy of the track circuit. When a train enters the section, its metal wheels and axles provide a low‐resistance path from rail to rail for the feed energy, greatly reducing or eliminating energy at the relay end that would be available for the detection device. The device then becomes de‐energized and indicates occupancy of the section. The track circuit status is used by the signal system to provide safe separation between trains and other safety functions. Note that under failure conditions, such as a broken wire, disconnected wire, missing feed, blown fuse, broken rail, etc., the circuit opens. The detection device de‐energizes and indicates occupancy even though there may not be a train present. This is a safe failure since it will be assumed by the signal system that there is a train occupying the section, keeping other trains a safe distance away. A track is divided into a continuous sequence of track circuits arranged end‐to‐end. Each circuit may also be referred to as a track section, or section. One or more track sections comprise a block whose entrance is governed by a signal. Track circuits are physically and electrically isolated from each other with insulated joints in one or both rails at each end. If insulated joints are in both rails, impedance bonds are needed at track circuit boundaries to allow traction (vehicle motor)

Read the entire page →

From page 10...

... SECTION 5 – SECONDARY TRAIN DETECTION/PROTECTION SYSTEMS 10 • Coded: The steady energy used in the non‐coded track circuit is modulated at certain rates. The modulation rates represent wayside‐to‐train information sent from the feed end toward receiving equipment on a train for transmission of information such as speed codes in conjunction with non‐ CBTC automatic train control and onboard speed enforcement. • Audio frequency (AF)

Read the entire page →

From page 11...

... SECTION 5 – SECONDARY TRAIN DETECTION/PROTECTION SYSTEMS 11 Compared to track circuits, there are few restrictions on the placement of axle counters. Track circuits use the rails as part of the circuit; axle counters do not. The rails are only used for mechanical mounting of the wheel detectors. Therefore, there is no concern for ballast leakage or rail resistance; little concern for traction current interference; no need for modifying the rail (or compromising its structural integrity) for insulated joints or to connect track wires and impedance bond cables. Since axle counters do not know the absolute state of their track section when they are powered up, there must be an initialization process which involves intervention of humans who know the state of the section. This must be done only when the section is truly clear and may require field confirmation. This may also require the first train after reset to enter and leave the track section -- while sweeping the section visually -- before accepting the axle counter state as valid. Manual intervention might also be needed in the case of a disturbed section, as might happen if the number of leaving wheels is more than the number of entering wheels since there cannot be a "negative" number of wheels left behind in the section. 5.2 Protection Functions Train detection lays the foundation for train protection. A train being detected is vitally mandatory for protection from a following train. An occupied block prevents the clearing of signals approaching the occupied block. In interlockings, detection additionally effects certain types of locking to provide route integrity, locking of movable rail in the route and under the train, and preventing release of said locking before it is safe to do so. The following summarizes some of these functions. 5.2.1 Automatic Block Signal System Between interlockings, STD/PS provides protection where each signal's control is arranged such that it will display red if a block in advance is occupied. The spacing between the red signal and the beginning of the occupied block is sufficient to provide safe braking distance if a train ignores the red and passes it at maximum speed. The signal will display yellow if the block in advance is vacant, but the next signal in advance is red. It will display green if the next signal is permissive (green or yellow)

Read the entire page →

From page 12...

... SECTION 5 – SECONDARY TRAIN DETECTION/PROTECTION SYSTEMS 12 • Detector locking. Locks a switch while the track section that includes the switch is occupied. Prevents movement of the switch where such movement could cause a derailment. Release of detector locking is usually delayed to prevent premature unlocking due to momentary loss of shunt across the track circuit.

Read the entire page →

From page 13...

... SECTION 5 – SECONDARY TRAIN DETECTION/PROTECTION SYSTEMS 13 capable of an off‐peak level of revenue service (Category 1.A.2) , where a reduction in service is possible during a complete CBTC failure or to manage non‐CBTC equipped trains. Category 1.B includes STD/PS designed to handle a single non‐CBTC train. There are also different subcategories based on performance desired when handling a single non‐CBTC train. The first sub‐ category allows one single train per interstation (Category 1.B.1)

Read the entire page →

From page 14...

... • For tr • Secon Category • Signa • For tr • Less e • Secon Category per inters • Signa • For tr • Secon Dependin signals on 1.A.2)

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From page 15...

... Category between • Signa • For tr • Secon Category between • Signa • For tr • Secon Category specific h • No sig • Secon 1.B.2.1 – Sec interlockings ls at interlock ains operatin dary detectio 1.B.2.2 – Sec interlockings ls at interlock ains operatin dary detectio 1.B.3 – Secon eadway perf nals dary detectio ondary syste , with second ings g under STD/ n system pre ondary Syste , with second ings g under STD/ n system pre dary System ormance n system pre m designed t ary detectio PS, signals ar sent everyw Figure m designed ary detectio PS, signals ar sent only at Figure designed to sent everyw Figure SECTIO 15 o handle a s n method ev e usually not here 4: Category 1 to handle a s n method on e usually not interlockings 5: Category 1 handle a sin here 6: Category N 5 – SECONDAR ingle non‐CB erywhere enforced au .B.2.1 ingle non‐CB ly at interlo enforced au .B.2.2 gle non‐CBTC 1.B.3 Y TRAIN DETECTIO TC train, cap tomatically TC train, cap ckings tomatically train, witho N/PROTECTION S able of one t able of one t ut territory YSTEMS rain rain

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From page 16...

... SECTION 5 – SECONDARY TRAIN DETECTION/PROTECTION SYSTEMS 16 Category 2 – No STD/PS • Systems without STD/PS • No secondary detection system Switch position indicators showing the position of switches to manual drivers are usually used when no interlocking signals are present; however, they are not represented in the following figure. Figure 7: Category 2

Read the entire page →

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