INTRO: Use of open-standard data communications links and overlapping free-space radio coverage offers cost-effective low-maintenance automatic train control

OPENED on July 15, the 6·4 km Las Vegas Monorail is the first fully-automated line-haul rapid transit route in the USA to use wireless Communications-Based Train Control. Running along the Strip district, it connects the city’s convention centre with eight resort and hotel complexes.

Laid out as a pinched loop design for continuous running, the $650m line has been funded by a consortium of private-sector promoters. It is projected to carry 19 million passengers in its first year of operation, at a flat fare of $3·00. A fleet of nine four-car trains running at 4min headways offers a design capacity of up to 5000 passengers/h in each direction. End-to-end journey time is 14min including five intermediate stops, with trains running at up to 80 km/h.

The eight hotels served by the monorail contain over 24300 rooms, and a further 35000 rooms lie within a 450m radius of the seven stations. The line is also expected to carry other visitors and local residents who work along the route.

The monorail has been developed from a 1·6 km shuttle which opened in 1995 to link the MGM Grand and Bally’s Hotel. Legislation was passed by the state of Nevada in January 1997, allowing Clark County to grant a franchise for the private sector to own and operate a public monorail network. Las Vegas Monorail Co was created in May 2000 as a non-profit corporation, to take over and extend the monorail, which closed for rebuilding in January 2003.

The original promoters formed Transit System Management to oversee and manage the design and day-to-day operations. The Las Vegas Monorail Team was selected to build the line. LVMT includes Granite Construction, responsible for the guideway, stations, traction power and the Operations & Maintenance building, and Bombardier, which is responsible for the trains and control equipment. Bombardier also has a five-year contract to operate and maintain the line, with two optional five-year extensions.

Plans are already being developed to extend the line at both ends, firstly from Sahara Avenue to the city centre and subsequently from MGM Grand to McCarran International Airport.

On February 20 the Regional Transportation Commission of Southern Nevada announced that the Federal Transit Administration had approved an initial US$20m towards construction of the city centre extension by 2008. RTC General Manager Jacob Snow said around one-third of the $454m cost will come from bonds similar to those that funded the initial line. Another third will come from a federal low-interest loan, and the remainder from federal grants.

Radio-based CBTC

Based on criteria including system-wide reliability, ease of installation and maintenance, and low life-cycle costs, LVTM selected Alcatel’s SelTrac¨ S40 open-standards radio communications-based train control to provide Automatic Train Operation, Protection and Supervision.

Alcatel favours open-standard data communication technology and IEEE standards, which allow operators such as RATP in Paris, KNR in South Korea and MTRCorp in Hong Kong to source components from different suppliers (RG 6.02 p307). Las Vegas is the first application of the company’s wireless network technology, well-proven in other industries, which uses frequency-hopping spread-spectrum radio modulation at 2·4GHz for train-to-track communication, and ’virtual block’ methodology to ensure a minimum safe vehicle separation.

Eliminating track circuits and transmission loops reduces the amount of lineside equipment, and reduces the need for maintenance access to the monorail beam. Use of ’free space’ wireless communication has the added benefit of providing full redundancy through overlapping radio coverage.

The vehicle-centric virtual block and interlocking logic is built into software, allowing optimisation of the blocks to maximise throughput. The monorail is designed to permit 90sec headways if more trains are added in the future.

Each trainset has a radio at each end, connected to a Vehicle On-Board Control unit that provides ATP for speed enforcement, and ATO functions such as speed control, station stopping, door control and performance regulation. Using the incoming radio signals, the VOBC interfaces with an on-board digital network and continuously reports train speed and position back to the lineside control units. These relay the information back to the control centre, where the supervisory staff also control other functions using Alcatel’s NetTrac MT operations management system.

Data communication system

LVM uses Alcatel’s ComTrac radio-based data communication system. Fully open-standard, using commercially-available off-the-shelf equipment, the DCS network consists of three main elements: the free-space radio link, a lineside network and a separate security system.

Lineside Access Points consisting of a radio and antenna are located adjacent to the guideway at regular intervals. An IEEE 802.3 standard Ethernet IP network extends the full length of the line. Ethernet switches at each station provide an interface with the control subsystems. Vehicle detection uses commercially-available transponders located at regular intervals along the guideway; these are read by the VOBC and the details passed by radio to the APs for transmission back to the OCC via an optic fibre backbone.

All subsystems communicate with the network through security devices. These use open-standard IPSec and Internet Key Exchange protocols for dynamic data key exchange. All data that cannot be authenticated is discarded.

Alcatel believes that the use of readily-available non-proprietary components will allow any or all of the independent subsystems to be upgraded or replaced in the future, without impacting on the rest of the train control system.

Most radio-based CBTC systems now in use rely on track-mounted cables wired to base stations. This means that a single-point failure could shut down a section of track up to 1 km long unless additional redundancy is incorporated.

The low-maintenance access points in Las Vegas provide overlapping radio cells for redundancy. In the event that one AP fails, trains can still communicate with the adjacent APs thanks to the overlapping coverage, ensuring that train control remains unaffected while the failure is pinpointed and rectified. The equipment is designed for rapid replacement, but the built-in redundancy means that repairs can usually be left until the next maintenance period.

According to Alcatel, the use of open standards means the network can be extended without the need for changes to track circuits or signal sections. There is an easy migration path to increase the communications bandwidth, offering the operator the potential to overlay other applications, such as security, system management or passenger information. The communications network could also carry commercial traffic, perhaps charged on a time-usage basis, which would allow the operator to gain value from the initial investment.

CAPTION: Revenue service on the Las Vegas Monorail began on July 15, following a formal inauguration on the previous day (RG 8.04 p451) Photo:Julian Wolinsky

CAPTION: BELOW: Supervisory staff at the LVM operations control centre will oversee the performance of the automated trains and other support systems using Alcatel’s NetTrac MT operations management system

BELOWRIGHT: Radio antenna for the Lineside Access Points are located adjacent to the guideway, linked by an optic fibre communications backbone. Vehicle detection uses transponders at intervals along the route

CAPTION: The use of Internet Prototcol for the communications links reduces the complexity of the interfaces between different systems and permits easy expansion