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From page 52... ... SECTION 10 52 Choosing the Secondary Method of Detection When the transit agency decides to implement some type of secondary detection, a selection must be made as to the type of equipment to be used. This section provides information to help transit agencies make this selection. Unlike the decision regarding the functional use of an STD/PS, choosing between track circuits and axle counters is not influenced by the required functionality of the signaling system. The decision is based on regulatory and technical factors. Track circuits and axle counters both satisfy the goal of detecting train occupancy. The principles for each method are described in Section 5 – Secondary Train Detection/Protection Systems. This section presents the benefits and limitations of each type of method. The influence of this selection on CBTC projects is also presented. 10.1 Secondary Detection System Layout Authorizing initial CBTC train movement and providing train separation with non‐CBTC trains are two of the CBTC core functions that have a direct impact on the implementation of the secondary detection system. The number of detection devices is based on the desired performance of those functions. 10.1.1 Authorizing Initial CBTC Train Movement In systems that feature a secondary detection method, the detection devices are used to ensure that there is no obstruction on the track around the CBTC train before authorizing CBTC train movement. The obstruction could be a non‐CBTC train such as a train with CBTC failure or a work train. The wayside controller uses the location reported by the CBTC trains and the knowledge of the secondary detection device layout to confirm that no "hidden" train is present before issuing a movement authority limit to the CBTC train. This function is discussed in Section 8.5 – Minimum Non‐Equipped Train Length Issue. Having more detection equipment means that train initialization can be performed at more locations. This is particularly important for managing the recovery of a train with CBTC failure or recovery of a wayside controller failure. On projects without STD/PS, the initialization of the train relies on operating procedures. 10.1.2 Providing Train Separation with Non‐CBTC Trains For projects with detection of non‐CBTC trains, CBTC allows CBTC trains to follow non‐CBTC trains using the occupancy status of each block. Since no information is received by the wayside controller regarding the non‐CBTC trains, CBTC keeps a vacant buffer between non‐CBTC trains and following CBTC trains. Having more detection device equipment means that CBTC trains would be able to follow non‐CBTC trains more closely. This function is also important for managing trains when a train experiences a CBTC failure. Read the entire page →
From page 53... ... SECTION 10 – CHOOSING THE SECONDARY METHOD OF DETECTION 53 10.2 Comparison Between Track Circuits and Axle Counters Table 14: Track Circuits vs. Axle Counters The asterisk (* Read the entire page →
From page 54... ... SECTION 10 – CHOOSING THE SECONDARY METHOD OF DETECTION 54 As shown in Table 14, the axle counter technology has a distinct overall advantage. For the criteria where track circuits have an advantage:  Hazards from vehicles that enter upon the track in the middle of a section can be mitigated by procedure.  The initialization and reset procedures for axle counters are a burden during failure scenarios, and not as part of normal operation. Read the entire page →
From page 55... ... SECTION 10 – CHOOSING THE SECONDARY METHOD OF DETECTION 55 10.3 Industry Survey Based on feedback from more than 70 CBTC projects around the world, the industry survey revealed that among the projects which implemented STD/PS:  39% of projects use track circuits  61% of projects use axle counters The few projects using both axle counters and track circuits were not considered to derive these numbers. Secondary methods of detection have shifted from track circuits to axle counters in recent decades. All CBTC suppliers can now provide both options and have project experience using track circuits and axle counters. The percentage shifted over time: Before 2005, among projects with STD/PS:  91% of projects use track circuits  9% of projects use axle counters After 2005, among projects with STD/PS:  29% of projects use track circuits  71% of projects use axle counters Because CBTC has become the most popular technology for mass transit, the number of projects since 2005 has increased significantly. The percentages among all surveyed projects (39% with track circuits, 61% with axle counters) are closer to the percentages of projects after 2005 (29% with track circuits, 71% with axle counters) Read the entire page →
From page 56... ... SECTION 10 – CHOOSING THE SECONDARY METHOD OF DETECTION 56 Table 15: Type of Secondary Detection Equipment in Different Categories of CBTC Projects Type Category Type Comment from the industry survey on the detection method Systems with STD/PS 1.A Secondary System capable of revenue service 1.A.1 Secondary System capable of peak revenue service Track circuits only 1.A.2 Secondary System capable of off‐peak revenue service Track circuits only 1.B Secondary System designed to handle a single non‐CBTC train 1.B.1 Capable of one train per interstation Majority with axle counters and a few with track circuits 1.B.2 Capable of one train in between two interlockings Majority with axle counters and a few legacy projects with track circuits 1.B.2.1 With detection devices everywhere Majority with axle counters and a few projects with track circuits 1.B.2.2 With detection devices only at interlockings Usually with track circuits or with both track circuits and axle counters 1.B.3 Without territory specific headway performance, with detection devices everywhere With axle counters and with track circuits Systems without STD/PS 2 No Secondary System Read the entire page →

From page 52...

... SECTION 10 52 Choosing the Secondary Method of Detection When the transit agency decides to implement some type of secondary detection, a selection must be made as to the type of equipment to be used. This section provides information to help transit agencies make this selection. Unlike the decision regarding the functional use of an STD/PS, choosing between track circuits and axle counters is not influenced by the required functionality of the signaling system. The decision is based on regulatory and technical factors. Track circuits and axle counters both satisfy the goal of detecting train occupancy. The principles for each method are described in Section 5 – Secondary Train Detection/Protection Systems. This section presents the benefits and limitations of each type of method. The influence of this selection on CBTC projects is also presented. 10.1 Secondary Detection System Layout Authorizing initial CBTC train movement and providing train separation with non‐CBTC trains are two of the CBTC core functions that have a direct impact on the implementation of the secondary detection system. The number of detection devices is based on the desired performance of those functions. 10.1.1 Authorizing Initial CBTC Train Movement In systems that feature a secondary detection method, the detection devices are used to ensure that there is no obstruction on the track around the CBTC train before authorizing CBTC train movement. The obstruction could be a non‐CBTC train such as a train with CBTC failure or a work train. The wayside controller uses the location reported by the CBTC trains and the knowledge of the secondary detection device layout to confirm that no "hidden" train is present before issuing a movement authority limit to the CBTC train. This function is discussed in Section 8.5 – Minimum Non‐Equipped Train Length Issue. Having more detection equipment means that train initialization can be performed at more locations. This is particularly important for managing the recovery of a train with CBTC failure or recovery of a wayside controller failure. On projects without STD/PS, the initialization of the train relies on operating procedures. 10.1.2 Providing Train Separation with Non‐CBTC Trains For projects with detection of non‐CBTC trains, CBTC allows CBTC trains to follow non‐CBTC trains using the occupancy status of each block. Since no information is received by the wayside controller regarding the non‐CBTC trains, CBTC keeps a vacant buffer between non‐CBTC trains and following CBTC trains. Having more detection device equipment means that CBTC trains would be able to follow non‐CBTC trains more closely. This function is also important for managing trains when a train experiences a CBTC failure.

Read the entire page →

From page 53...

... SECTION 10 – CHOOSING THE SECONDARY METHOD OF DETECTION 53 10.2 Comparison Between Track Circuits and Axle Counters Table 14: Track Circuits vs. Axle Counters The asterisk (*

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From page 54...

... SECTION 10 – CHOOSING THE SECONDARY METHOD OF DETECTION 54 As shown in Table 14, the axle counter technology has a distinct overall advantage. For the criteria where track circuits have an advantage:  Hazards from vehicles that enter upon the track in the middle of a section can be mitigated by procedure.  The initialization and reset procedures for axle counters are a burden during failure scenarios, and not as part of normal operation.

Read the entire page →

From page 55...

... SECTION 10 – CHOOSING THE SECONDARY METHOD OF DETECTION 55 10.3 Industry Survey Based on feedback from more than 70 CBTC projects around the world, the industry survey revealed that among the projects which implemented STD/PS:  39% of projects use track circuits  61% of projects use axle counters The few projects using both axle counters and track circuits were not considered to derive these numbers. Secondary methods of detection have shifted from track circuits to axle counters in recent decades. All CBTC suppliers can now provide both options and have project experience using track circuits and axle counters. The percentage shifted over time: Before 2005, among projects with STD/PS:  91% of projects use track circuits  9% of projects use axle counters After 2005, among projects with STD/PS:  29% of projects use track circuits  71% of projects use axle counters Because CBTC has become the most popular technology for mass transit, the number of projects since 2005 has increased significantly. The percentages among all surveyed projects (39% with track circuits, 61% with axle counters) are closer to the percentages of projects after 2005 (29% with track circuits, 71% with axle counters)

Read the entire page →

From page 56...

... SECTION 10 – CHOOSING THE SECONDARY METHOD OF DETECTION 56 Table 15: Type of Secondary Detection Equipment in Different Categories of CBTC Projects Type Category Type Comment from the industry survey on the detection method Systems with STD/PS 1.A Secondary System capable of revenue service 1.A.1 Secondary System capable of peak revenue service Track circuits only 1.A.2 Secondary System capable of off‐peak revenue service Track circuits only 1.B Secondary System designed to handle a single non‐CBTC train 1.B.1 Capable of one train per interstation Majority with axle counters and a few with track circuits 1.B.2 Capable of one train in between two interlockings Majority with axle counters and a few legacy projects with track circuits 1.B.2.1 With detection devices everywhere Majority with axle counters and a few projects with track circuits 1.B.2.2 With detection devices only at interlockings Usually with track circuits or with both track circuits and axle counters 1.B.3 Without territory specific headway performance, with detection devices everywhere With axle counters and with track circuits Systems without STD/PS 2 No Secondary System

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