Technology

The 'Genius' Idea for Improving Rail Signaling Accuracy

Posted on May 31, 2018 by Robert James

NYCT Signal Maintainers perform scheduled replacement of relay equipment.
MTA New York City Transit/Marc A. Hermann
NYCT Signal Maintainers perform scheduled replacement of relay equipment.
MTA New York City Transit/Marc A. Hermann
The New York MTA Genius Transit Challenge awarded eight winners for presenting new and innovative ideas for improving the reliability of the New York City Subway system. As one of those eight winners, my proposal, focused on Ultra-Wideband wireless technology aiming to eliminate expensive signal equipment and improve accuracy. The novel part is applying a highway technology being deployed in large numbers to the rail signals application.

Ultra-Wideband (UWB) can provide five-centimeter accuracy location for all the cars in tunnels with very low cost to deploy.  When used with Connected Vehicle (CV) Dedicated Short Range Communications (DSRC) integrated with the signal system, it can provide much more accurate and responsive signaling than the conventional Communication Based Train Control (CBTC) systems. They can also be installed for a fraction of the cost of CBTC continuous-inductive technology due to the minimal need for track outages. It is also a standards-based technology in the surface roadway market that prevents the agency from being gauged by the high cost of the rail signaling system vendors.

There are some locations currently using this, or similar, technology. Vendors are unifying Positive Train Control (PTC), Collision Avoidance, and Worker Protection under a single solution and it is reportedly being deployed for MBTA in Boston and some freight rail systems. Port Authority of NY/NJ Exclusive Bus Lane (XBL) Automated Bus Project is beginning to automate buses in the Lincoln Tunnel using the same technology to increase current capacity/improve safety. The CV/UWB technology is a key component of this project. NYCDOT CV Pilot project showed five-centimeter accuracy with key enabling Ultra-wideband technology was possible in the urban canyon environment where GPS wasn’t available. Over the winter NYC Transit tested the technology for deployment on the subway trains and right-of-way and liked what they saw and awarded the idea for the signals area of the MTA Challenge.

What is UWB
So, what is UWB and how can it work for the New York City Subway system? Existing rail signaling systems rely on track circuits installed in the tracks to locate the trains. The problem with this old technology is that it only tells you that a train is occupying a block, which can be miles long in some locations. It also does not communicate speed. Some rail systems have added GPS to trains to provide better location and speed data, but this does not work in areas where satellites are obscured, such as urban canyons, tunnels, stations, and mountainous areas. GPS has not been shown as accurate enough to determine what track a train is on when there are parallel tracks without other means to assist in the location.

Ultra-wideband technology is a chip set that uses ultra-low power pulses to provide centimeter accuracy location through cooperative communications. It has widespread use in defense and mining applications and has begun to take off in the transportation arena. UWB provides the high accuracy location (<5cm) in real-time anywhere within the right-of-way. It also provides a continuous wayside to train communications.

The UWB transmitters would be installed on each car and their wayside units are typically integrated into the lighting every 50 to 100 meters in the tunnel and along the wayside. CV units are installed every 300 to 1,000 meters to communicate back to the signaling system. They can easily be installed in yards and other dark territories to light up the areas with very little cost.  

Having continuous knowledge of the high-accuracy vehicle locations and speed in the tunnels allows more advanced signal control systems such as PTC and CBTC to have key information to provide reduced train spacing allowing higher throughput. Existing CBTC systems cannot match the accuracy and ease of installation of this new concept. Also, existing location systems used with CBTC deployments install transponders in the tracks and rely on wheel-turn information to maintain a location estimate between transponders. CV/UWB can be quickly installed in the lighting system of the tunnel since it is a very small device and only needs two watts of power and no other wiring. It will maintain continuous location of any equipped object in the area along the right-of-way allowing it to be used for many more purposes in addition to signaling.

Precise asset management
In addition to the signaling system benefits, the system allows precise asset management along the right-of-way allowing a complete collection of all wayside assets, as well as providing real-time locations of all the rolling stock and light up dark territories. This is a huge benefit to the operations control centers, the yard masters, the wayside, and rolling stock maintainers. This can also be used tracking workers in or near the right-of-way and alerting the workers, and train crew, when trains are approaching an active work zone. It allows drones to be dispatched quickly into the tunnels to allow track inspections for maintenance personnel to get eyes in the field very quickly.

Train spacing will also be an area affected by the use of this technology. With continuous location and speed knowledge, the train operator, as well as the signaling system, will be able to know the surrounding vehicles and be able to determine what actions to take, immediately reducing the spacing requirements. The brick wall spacing can be eased because you know any change in velocity and can incorporate that into your spacing algorithms. It can also be integrated into the existing fixed-block or moving-block signal system to provide better location and speed data for the train control dispatchers and better cab signaling for the train operators. Alternatively, this can be the backbone of a new CBTC system to replace the existing signaling.  

UWB has been proven to be reliable and resilient being designed to military specs due to the origins in the defense industry. Their cooperative communication also allows them to self-monitor and report any loss of devices. They are deployed redundantly so that that they can still operate with several individual failures.
 
Improve safety, cost-effective
UWB can also be used as an active radar with LIDAR-like resolution that can be used to improve safety. It can pick up other objects obscuring the tracks. The system also provides worker protection by tracking the workers when they are in or near

New CV/UWB CBTC vehicle interface.
New CV/UWB CBTC vehicle interface.
the right-of-way and can be used for warning the workers of approaching trains and alerting the train operators of fouled tracks ahead.

Not only can it improve safety, but the cost of these devices is much less expensive than traditional track circuits for obtaining location, and can do much more. Comparatively, estimates are $500 per UWB device and $1,200 per CV/UWB onboard device. They don’t require expensive wiring like other field systems and major track outages. As confidence grows in these devices, the track circuits can be replaced. This can save billions of dollars in deployment costs over current CBTC systems.

With the power of the UWB devices at only two watts, they are also a very small form factor. That is why it is so easy to integrate into existing tunnel lighting systems or power with solar panels and batteries outside tunnels. CV units are only five watts and are only located in the signal locations and station to provide central communications to the field. NYCDOT maintenance crew with very little training installed 25 units in the street lights of 10 blocks on 6th Ave in two hours. The diagram below shows the accuracy achieved in this deployment compared to the poor GPS performance even with dead reckoning. The UWB vendor has worked with several tunnel lighting companies to integrate their transponders into the lighting system. These can be installed as part of the normal lighting maintenance schedule. The speed and ease of these installations are a major benefit for the use of UWB devices in New York City Subway systems.

MTA has reportedly allocated a $160 million project to implement the first phase of deployment of this technology.  It offers the advantage of using standards-based technologies instead of proprietary solutions, and boasts many benefits to rail signaling, passenger communications, and right-of-way safety. It will also offer a much lower implementation cost than existing signaling systems.   

Robert James is Chief Engineer of Emerging Mobility for HNTB (www.hntb.com).

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