Cities that invested in the construction of a new metro system in recent years encountered both advantages and drawbacks compared to cities that built systems a hundred or so years ago. Metro systems of old still needed to dig tunnels in city centres but the disruption to everyday life did not have the constraints put upon it that would occur nowadays. Cities were also smaller and the metro network would be used to encourage development in the suburbs and adjacent countryside, where building the rail infrastructure would be relatively simple. The metro would thus be an engine for growth.
In more recent times, metros have taken on a different role and are built primarily to ease the problems of traffic and urban congestion. This means no green field sites for construction plus having to comply with current day environmental and safety requirements while having minimal impact on the business life of the city.
The plus side is that the lessons of metro operation elsewhere can be taken on board and the layout and capacity of the system can be accurately modelled. It also means that the use of current technology for all aspects of operation can be designed in from the outset and not have to be bolted on as an afterthought.
Copenhagen is one such city, so the rail engineer visited Metro headquarters to learn how it came about and the service that it offers.
Copenhagen’s current line
When the Øresund link from Copenhagen (København) to Malmö (Sweden’s 3rd City) was being planned, it was realised that this would bring a new influx of business and visitors to the city. Access to Malmö from the wider world would likely be via Copenhagen airport, which in turn would encourage people to visit Copenhagen as well. Thus some form of enhanced urban transport would be required and so a metro line was conceived.Authorised in 1992, the planning of the route, with all the legal processes that were required, took until 1997 before construction could start. The first section opened in 2002 from Vestamager in the south to Vanløse in the west, including a short section from Fasanvej to Frederiksberg which was a former S-tog (S-train) line. An extension line from the city centre station of Christianshavn to the airport was opened in 2007, the junction being in a tunnel section.Construction work was carried out by a consortium of contractors with the control and communications element being awarded to Ansaldo STS. Owned by the Copenhagen Municipality, the system is in effect a Y layout and is operated as two routes, M1 and M2, serving the two prongs of the Y. It is 21km total length with 10km of tunnel, 12km on either elevated viaducts, embankments or level ground, 22 stations of which nine are underground and is double track throughout.
The elevated viaduct sections have high level stations accessed by escalators. Platform screen doors are provided only in the underground stations.
Thirty-four three-car articulated trains, each 39 metres long, plus three engineer’s vehicles comprise the rolling stock fleet. Electric traction is the classic 750V DC third-rail system but with the trains converting this for 3-phase AC motors. A two-minute headway is achieved in the city centre section at rush hours, reducing to four minutes off-peak. The line is unusual in offering a 24 hour, 7 days a week service, the train frequency at night being every 15 – 20 minutes.
The control centre and maintenance depot are situated at the south end of the line near to Ørestad station. Daily cleaning and external washing are carried out here as well as intermediate overhauls and piece part replacement when heavy maintenance is required. The line operation and maintenance is outsourced to Ansaldo STS which employs ‘Metro Service’ as its sub contractor, this being a consortium of firms both local and international with metro experience.
The signalling (more accurately control and communication) system was state of the art at the time of introduction. As would be expected, the trains are driverless using an Automatic Train Control system that comprises ATS (Automatic Train Supervision) plus ATO (Automatic Train Operation) with ATP (Automatic Train Protection), the latter being the safety critical element. The system is fixed block but with moving block capability around station areas.
Reliability and availability were seen as all important so the system uses a resilient fibre- optic network with a distributed architecture. The whole system is designed for redundancy and this includes the train equipment. Train movement commands are transmitted via jointless track circuits operating in the 9.5kHz to 16.7kHz range upon which digital codes are picked up by the trains.
Traction return current is via only one rail using impedance bonds although there is some cross bonding between adjacent tracks. Interlockings of the ‘Microlok’ type are provided at stations so as to control points at terminal stations, junctions and in the event of trains having to be turned back at intermediate stations to cater for service disruption or engineering work.
Track loops are installed at station sites for non vital activity such as door control. A 1.1 metre tolerance exists for platform stopping accuracy. Trains are fitted with an emergency driver’s panel in the event of system failure. The service availability achieves around 98.6%.
Expanding the network
With the success of the first line, it was almost inevitable that the city authorities would wish to expand the metro network. The original line served the city centre, some business areas and the airport but strangely not the main Copenhagen railway station.
A second line has since been authorised in 2011, again with the contract for control and communication being awarded to Ansaldo STS but using the very latest CBTC (Communication Based Train Control) technology.
The line will be entirely in tunnel and will form a 15.5km ring to be known as ‘Cityringen’. Because of the significant tunnel work needed, it will take some time to build and the in- service date will not be until 2018. 28 trains are to be provided and will also provide a 24 hour, 7 days a week service. The line will provide an interchange with the main line station and an extension line going eastwards from the ring is already planned.
The CBTC system will differ considerably from that used on the first line and will be based upon continuous train-to-trackside communication via radio with the trains determining their own position within the system. Reference points will come from ‘Track 4 Tags’, in effect a proprietary version of a balise. Both train and trackside will be equipped with vital processors to ensure the highest level of operational safety. The radio system will also facilitate real time video images from the passenger cars.
Planning for failure
Maximum train speed will be 90kph with a minimum headway of 75 seconds. The line will be commissioned for UTO (Unattended Train Operation) although it will be possible to drive trains manually at normal speeds, protection being afforded from the ATP element of the CBTC system. In the event of total system failure, the trains will be capable of being moved at slow speed on the basis of ‘drive on sight’.
The system is being designed to prevent trains being stopped in tunnels midway between stations and thus despatch of a train will not generally be permitted unless there is a clear path to the next stopping point. This will thus protect against situations such as a failed train ahead, detection of fire or smoke conditions, platform screen doors failed and such like. Rescue trolleys will be available at key points for the use of emergency services.
In the failed train situation, it is planned that rescue will be by the following train being allowed under controlled conditions to couple up to it and push the failed train to the next station. Both trains would then be cleared of passengers at that point, whence the two trains will proceed to a stabling siding or depot.
Great emphasis is being put on regular and accurate communication to passengers in such a situation by both video and audio messaging. Part of this will be the provision of help call points on every train.
Very shortly, Copenhagen will have two metro lines which are entirely incompatible with each other. The only common element will be the cross passages at interchange stations. This demonstrates the rapid technological development that has taken place in the last 10 years. Being ‘closed’ systems, the incompatibility does not matter too much other than the enforced duplication of spares, training and general staff expertise.
Other metro systems are experiencing similar challenges, London being one of them where different lines are being upgraded with systems from different suppliers, none of which have common engineering philosophies except at the highest functional level. CBTC technology is supplied by all the major signalling companies and, whilst all of them provide more or less the same operational features, there is no commonality in design, equipment, or construction. There have been calls for the industry to produce a common specification for CBTC so as to achieve a degree of interoperability or even inter-changeability but little progress has been made.
Compare this scenario to the main line rail situation and one can see why it has taken so long to achieve effective interoperability with ERTMS. One can only hope that the railway control and communication mindset will one day come to terms with the need for both forward and backward compatibility as product technology advances plus some much needed co-operation between suppliers to produce common system designs.
Copenhagen can be justly proud of its expanding metro system, it is well used and performs a valuable service for the city. Coming to terms with the technology will however be ongoing for some time.