SelTrac

SelTrac is a digital signalling technology used to control the movements of rail vehicles originally developed by Alcatel. SelTrac is now sold by Thales.

SelTrac Communications-Based Train Control (CBTC) technology

SelTrac is a family of three different train control products from Thales. Capabilities range from simple train speed limiting to fully managed train control.

Product family

SelTrac LS

SelTrac LS is a logic block based train control system.

SelTrac MS

SelTrac MS is a more advanced fixed-block train control system.

SelTrac IS

SelTrac IS is a fully moving-block automatic train control system. To upgrade existing fixed-block systems, installation is performed as an overlay in parallel with the existing system. A cut-over strategy allows operators to phase in the new system. However, such parallel deployment proved to be a time consuming, costly, and unreliable way of deploying SelTrac. See also the San Francisco Muni Meltdown of 1998 that occurred as a result of an attempted parallel deployment.

How it works

Inductive loop

SelTrac IS uses inductive loops for both continuous bi-directional communication from trains to wayside and train positioning. The inductive loop cable consists of a stranded copper core with an insulating and protective outer sheath. The cable serves as both transmit and receive medium for the inductive loop communication system. Insulated twisted copper core loops are laid between the full length of the running rails and transposed (cross-over) every 25 meters for ground reference calculations. Vehicle On-Board Controllers (VOBCs) detect the signal phase shift at the cross-over and count them. This information is combined with axle-mounted tachometer outputs to provide highly accurate train position measurement.The inductive loop setup operates on a low frequency: Continuous packet data transmission at the rate of 1200 bit/s (carrier frequency of 36 kHz) from wayside to vehicle and 600 bit/s (carrier frequency of 56 kHz) from vehicle to wayside. Separate antennae are used for transmission and reception.The selection of frequencies and transmission rates allows for high data communications capacity, thus overcoming fundamental limitations of coded track circuits. Transmitter and receiver circuitry can be upgraded using standard COTS components.

Radio frequency

* Operates “free space propagation” on the the 2.4 GHz or 5.8 GHz frequency (ISM) WLAN system.
* Radios operate using IEEE standard 802.11x, which supports seamless fragmentation and assembly of data packets while maintaining sequential transmission.
* The standard is fully compatible with the universal IEEE 802.3 Ethernet standard.
* Radio access Points (APs) are installed on trackside every 250 metres typically for full coverage.
* Mobile radios are placed at each end of the vehicle. Wayside control units are tied into a fibre optic backbone with network switches. Each trackside AP is connected to a switch in an overlapping pattern to ensure redundancy. Each train has more than one link to the wayside. As a train moves down the track, the link changes from one AP to the next.
* Transponder tags on track-bed every 25-150 metres typically and tachometer on vehicle to verify vehicle position.
* Thales’ ComTrac DCS network is an Ethernet LAN implemented according to the 802.3 standard. The network also employs the 802.11 FHSS standard for implementing the radio portion of this network. The radio operates in the 2.4 GHz ISM radio band.
* The transmission rate of the 802.11 radio frequency-hopping system is 1 Mbit/s, and each radio which is capable of supporting more than 600 kbit/s of single access (uni-directional) data throughput, or more than 200 kbit/s of multi-user bi-directional traffic data throughput.

Problems

Coping with new routes

Despite Alcatel's claims of the flexibility afforded by using standards based equipment, SelTrac S40 is not terribly flexible in a number of ways. The most obvious problem is that the routes and terminus points are hardcoded into the central control program. [cite web
url = http://www.sfmunicentral.com/
title = Live Snapshots of Muni Subway - Frequently Asked Questions
publisher = San Francisco Municipal Railway
accessmonthday = May 17
accessyear = 2008]

In the San Francisco deployment of SelTrac S40, this is quite obvious in two ways. The first is through sfmunicentral.com. Routes that were not in service at the time of the SelTrac deployment (1999), such as the S Castro Shuttle and T Third Street, appear on the SelTrac display either without a route (and instead are marked with an asterisk) or with the wrong route (usually the K Ingleside). This is also apparent to MUNI passengers because trains on the new routes are not announced properly by the overhead signs. Instead station personnel must announce the trains manually.

Additionally, SelTrac is unable to cope with turning trains around at different parts along the route. The end result is that all trains are announced to passengers as running to the end of their respective lines regardless of the intended terminus.

Dangerous brake control

Also in San Francisco, the SelTrac deployment was simply unable to cope with applying the service brakes on a downward grade. [cite web
url = http://www.lumiere.net/home/forums/archives/rescuemuni/0693.html
title = RE: EBs in the Subway--The problem continues!
publisher = Rescue MUNI
author = Peter D. Ehrlich
accessmonthday = May 16
accessyear = 2008] [cite web
url = http://www.lumiere.net/home/forums/archives/rescuemuni/0883.html
title = Re: EBs in the Subway--ARRGH
publisher = Rescue MUNI
author = Peter D. Ehrlich
accessmonthday = May 16
accessyear = 2008] The result was that SelTrac would unnecessarily apply the emergency brakes, throwing passengers to the ground. The work around, called EBALD (Emergency Brake Acceleration Limiting Device), was to reduce the effectiveness of the track brakes when applied by SelTrac. However, nearly ten years after its initial deployment passengers are routinely thrown to the ground with no warning. [cite web
url = http://groups.yahoo.com/group/rescuemuni/message/2069
title = Muni safety hour on the radio; emergency stops
publisher = Rescue MUNI
author = Christopher Beland
accessmonthday = May 16
accessyear = 2008] Occasionally injuries are severe enough to warrant hospitalization. [cite web
url = http://www.njudahchronicles.com/2008/02/injury_on_a_k_outbound_stops_m.html
title = Injury on a K Outbound Stops MUNI Metro Traffic - Live Report
publisher = N Judah Chronicles
accessmonthday = May 16
accessyear = 2007]

Coping with multiple car trains

SelTrac uses the wheel speed to calculate where the rail car is located. Because SelTrac must know precisely where each car is, it is unable to cope with trains comprised of vehicles with different sized wheels. In San Francisco, because Alcatel did not test every two car combination, the end result was that subway entry was often delayed or only possible in cutout mode.

SelTrac installations

SelTrac is installed in many railways around the world, including the following:

* Ankara RT 1997 SelTrac IS ATO with Attendant Bombardier H6
* Beijing Line 4 2009 SelTrac MS ATO with Attendant Siemens/Tsing Dao
* Berlin Metro 1982 SelTrac ZB ATO with Attendant Siemens
* Busan-Gimhae 2011 SelTrac LS Driverless ATO Rotem
* Canadian Pacific 1990 ATCS Radio-Based Train Protection
* Detroit DPM 1987 SelTrac IS Driverless ATO UTDC/Bombardier
* Dubai LR – Red and Green Lines 2009 SelTrac IS Driverless ATO Kinki Sharyo
* Duisburg Metro 1992 SelTrac ZB ATO with Attendant Siemens/Vossloh
* Dusseldorf Metro 1988 SelTrac ZB ATO with Attendant Siemens/Vossloh
* Guangzhou Line 3 2006 SelTrac IS ATO with Attendant Siemens
* Hong Kong MTR West Rail Line 2003 SelTrac IS ATO with Attendant Kawasaki
* Hong Kong MTR Ma On Shan Line 2004 SelTrac IS ATO with Attendant Kawasaki
* Hong Kong MTR Kowloon Southern Link (West Rail Line) 2009 SelTrac IS ATO with Attendant Kawasaki
* Hong Kong MTR Disneyland Resort Line 2005 SelTrac LS Driverless ATO Cammell
* Jacksonville ASE 1998 SelTrac LS Driverless ATO Bombardier
* JFK International Airport AirTrain APM 2003 SelTrac IS Driverless ATO Bombardier MK II
* Kuala Lumpur LRT II 1998 SelTrac IS Driverless ATO Bombardier
* Las Vegas Monorail 2004 SelTrac LS Driverless ATO Bombardier
* London Docklands Light Railway 1995 SelTrac IS ATO with Attendant BN/Bombardier
* Lewisham Extension 1999
* London City Airport Extension 2005
* Woolwich Extension 2008
* London Underground – Jubilee Line 2009 SelTrac IS ATO with Attendant Alstom
* London Underground - Northern Line 2011
* London Underground - Piccadilly Line 2014
* Mulheim/Ruhr Metro 1999 SelTrac ZB ATO with Attendant Seimens/Vossloh
* Newark International Airport APM 1996 SelTrac LS Driverless ATO Von Roll/Bombardier; Northeast Corridor Extension 2001
* New York City Transit Canarsie – Phase III 2006 Interoperability Program
* Paris Line 13 – Ouragan 2010 SelTrac MS ATO with Attendant Alstom/Ansaldo
* Quebec Cartier Railway 1992 NetTrac MT Dispatch System
* San Francisco Municipal Railway 1997 SelTrac IS ATO with Attendant Boeing/Ansaldobreda
* Seoul KNR Bundang Commuter 2006 SelTrac LS ATO with Attendant Rotem
* Shanghai – Line 6 2007 SelTrac MS ATO with Attendant Alstom (part)
* Shanghai Line 8 2007 SelTrac MS ATO with Attendant Alstom (part)
* Shanghai Line 9 2007 SelTrac MS ATO with Attendant Bombardier (part)
* Shanghai Line 7 2009 SelTrac MS ATO with Attendant
* Shanghai Sin Bundang Line, Seoul, 2011 SelTrac IS Driverless ATO Rotem
* Tampa International Airport APM 1992 SelTrac LS Driverless ATO TGI/Bombardier
* Toronto Scarborough RT Line 1985 SelTrac IS ATO with Attendant UTDC/Bombardier
* Toronto Subway 2008 SelTrac MS Speed/Signal Safeguard Cancar/Bombardier
* Vancouver Canada Line 2009 SelTrac IS Driverless ATO Rotem
* Vancouver SkyTrain – Expo Line 1986 SelTrac IS Driverless ATO UTDC/Bombardier
* Millennium Line 2002 SelTrac IS Driverless ATO Bombardier MK II
* Walt Disney World Monorail 1989 SelTrac MS ATP Disney/TGI
* Washington Dulles Airport APM 2009 SelTrac LS Driverless ATO Sumitomo/MHI
* Wuhan LRT 2004 SelTrac IS ATO with Attendant Changchun Car Co.

See also

* [http://www.xs4all.nl/~dodger/tech.htm SelTrac technology]
* [http://www.questertangent.com/upload/docs/QTC_Transit_Projects_List_June_06.pdf EBALD]
* [http://www.rescuemuni.org/meltdown/meltdown.html MUNI Meltdown Analysis]
* [http://www.njudahchronicles.com/2008/02/injury_on_a_k_outbound_stops_m.html Injuries as a result of SelTrac]

References