Advanced LRT Control
In the recent years, number of U.S. and Canadian cities, including Great Toronto Area Ontario, there is a great revival for mass transti, particularly Light Raild Train transit. A lightweight metropolitan electric railway system characterized by its ability to operate single cars or short trains along exclusive right-of-way at street level. These vehicles are usually powered by overhead electrical wires, and offer a frequent, fast, reliable, comfortable and high quality service that is environmentally sustainable.
Advanced Light Rapid Transit or ALRT is the name given to a rapid transit system manufactured by Bombardier Transportation, originally named ICTS (for 'Intermediate Capacity Transit System'), and is also commonly referred to as 'advanced rapid transit'. Light Rail Transit (LRT) is made up of modern, electricity-powered Light Rail Vehicles (LRV) that carry passengers in dedicated lanes, separated from motor vehicle traffic. Like a subway, LRVs can be boarded at all doors, sometimes travel underground, carry large numbers of passengers and operate at high speeds. It can also operate at street level, have more frequent stops and cost much less to build and maintain than subways. LRVs have no local emissions, since they are powered by electricity, and can be run on renewable energy like wind and solar. The latest and greatest LRT vehicles are fully accessible for wheel-chairs, strollers, and shopping carts, as well as faster boarding through multiple doors.
Rail and mass transit systems rely on signal systems of various types to provide safety in their operations. These operations enforce train separation as they operate. The proper design and use of the signaling determine the overall capacity of the system in terms of headway and throughput efficiency.
Safety and Enforcement in LRT Apps
Recent legislations enacted in North america have mandated the installation of Positive Train Control (PTC) on virtually all Class 1 mainline and Passenger railroads (A Class I railroad is defined as having annual revenues of at least $250M). PTC is a form of train control generally based on the Global Positioning System (GPS) where trains determine their location. Movement authorities are transmitted to trains over data radio networks, and trains ping wayside devices to check the route ahead.
PTC type systems are being developed throughout the world with similar architecture. The PTC is currently being developed for before the mandated 2015 time limit. The braking algorithm being progressed involves specific inputs such as speed, train weight and alignment. This is called "Adaptive Braking" in that it calculates a different solution based on the data on hand. LRT train control systems recently deployed have tended to include some sort of enforcement of either wayside signals and/or civil speeds. Some deployments have installed cab signals for civil and signal enforcement, while others have installed Trip Stop systems for mainly signal protection. This enhances the safety of train operation in terms of collision avoidance and operating speeds, but adds significantly to equipment capital and maintenance costs.
Modern LRT systems require several features that are offered to the riding public that are incorporated in advanced train control and management systems generally associated with heavy rail metros. Some of these features include:
- Collision Avoidance
- Automatic Routing at junctions
- Train to Wayside Communications (TWC) devices for station and on board announcements
- Fixed highway crossing starts for flashing light signals and gate (FLS&G) and preemption
- Near side stations with timed approach and reactivation of FLS&G.
These functions are realized in conventional signaling, generally with cab signals and ancillary equipment. However, Communications Based Train Control systems offer these functions with a different concept that can reduce the wayside equipment requirements. Moving forward, LRT properties generally cannot afford the cost of CBTC systems, but could use key features such as:
- Packaged interfaces to Public Address and Customer Information Systems (PA/CIS)
- Automatic Vehicle Location (AVL) from precise location determination sub systems within CBTC
- Automatic Train Operation/Driverless Train Operation/Unattended Train Operation (ATO/DTO/UTO)
- Platform Screen Doors (PSD) interfaces.
Positive Train Control offers a potential solution to LRT operations, however PTC from the Class 1 railroad perspective (using the I-ETMS approach) is
still largely a development project. This means that adding features that would allow full integration into the LRT environment will likely not take place until after the mandated deployment date of December 31, 2015.
We have deferentiated four approaches for the PCT Types. The first one is a Non-vital overlay. A Non-Vital Overlay PTC system is designed to enforce features of an existing method of operation and must be shown to reliably execute the functions set with at least an 80 percent reduction of the risk associated with accidents. The system enforces an underlying system such as conventional wayside signals. Sensors are configured in such a way as to determine what aspects signals display, or what position switches are in.
The second is a Vital Overlay. A Vital Overlay PTC system is similar to a Non-Vitalv Overlay in that it must reliably execute the functions and have sufficient documentation to demonstrate fulfillment of the safety assurance principles required. A Vital Overlay system is essentially the same as a Non-Vital Overlay system that is realizes with vital processes. This represents the safety critical nature of conventional train control and greatly enhances safety.
The third PTC type is Stand-alone. A Stand alone PTC system is a replacement for an existing signal or train control system, or otherwise changes to the existing method of operations. A Vital Stand Alone system has no underlying system and directly controls the enforcement of civil speeds, train separation, etc. without any other input. This is similar to CBTC systems that operate on moving or virtual block arrangement.
The last type is a Mixed PTC system. A Mixed PTC system combines Stand-Alone, Vital, or Non-Vital characteristics while possessing appropriate structuring of the safety case and analysis.
Advanced PTC for Light Rail
Advanced signal solutions for LRT systems discussed here offer many advantages in terms of operations, safety, and capacity. Key factors in choosing PTC for LRT train control have been discussed, but other considerations include:
- There will be a very large installed base of equipment that provides a stable market
- Transit agencies will be able to take advantage of future development for both hardware and software as the PTC products mature
- Since PTC will be common throughout the U.S., utilizing the same PTC system may offer opportunities to eliminate Temporal Separation on joint use facilities. This would greatly benefit both the freight and transit operations
- Crossing starts, preemption and priority control of highway crossings can be based on prediction from the known parameters on the train as opposed to fixed locations. This can greatly enhance operations and interfaces to highway vehicular traffic
- The inherent position determination system can be used to replace Automatic Vehicle Location (AVL) systems and Train to Wayside Communications (TWC) loops currently in service. This can reduce the equpment and power cunsumption on LRT and provide pricise train annuncements on board and at stations
- Without the need for broken rail protection, track circuits will not be necessary. Singificant cost savings can result from reduced field equipment, but also form elimination of traction power bonding associated with track circuits and special track work, as well savings in installation labour.
The North American market is alredy adapting these technologies for other applicaitons in non-traditional modes, such as PTC as a collision avoidance system. In spite of additional costs, CBTC will be also applied to LRT system where GPS navigation is not possible or where near Metro capacity is required.
Although there will be a self sustaining market for PTC related equipment and development, PTC as an overlay will not provide the full benefit of the technologies capabilities but adaptable to transit needs. Transit applications offer an expanded, sustainable market for the future.