Square pegs in round holes: they don’t fit – at least not without a large hammer. The same principle works for the integration of light and heavy rail systems. Tramways are designed in isolation, they’re not intended to interact with trains or other operators.

On 10 December, Sheffield Supertram unveiled its first new tram-train. Creeping out of the main shed at Sheffield’s Nunnery Depot, it is the first of seven which are being built in Spain by Vossloh, which is now owned by Swiss manufacturer Stadler, as part of a joint two-year pilot tram-train programme being delivered by the Department for Transport (DfT), Stagecoach Supertram, Network Rail, Northern Rail and the South Yorkshire Passenger Transport Executive (SYPTE).

The introduction of tram-trains will allow Supertram services to travel on the national rail network. Passengers will be able to board one of the new vehicles at Sheffield Cathedral and travel directly to Parkgate Retail Centre in Rotherham, via Meadowhall South and Rotherham Central station, in about 25 minutes.

It is the first tram-train to be built for the UK, but the project is drawing on the experience of tram-train systems in Europe, specifically Karlsruhe. The Karlsruhe Model is often cited as the first tram-train system in Europe and has been the basis of other projects around the continent. The German city has also recently begun operating a new fleet of Vossloh Citylink tram-trains similar to those being trialled in Sheffield.

Although it will be the first tram-train vehicle to operate in the UK, the tram-train concept isn’t new to Britain. Manchester Metrolink trams run on what were the Bury-Victoria and Altrincham- Piccadilly lines connected by an on-street section of tramway through the city centre. As a result, the current Bombardier M5000 fleet have specially designed wheel profiles.

Working with the University of Huddersfield, which was also involved in Manchester Metrolink, Sheffield’s project team has developed a wheel that fits the rail head profiles of both systems, reducing wear rates and mitigating against the risk of derailment, specifically around switches and crossings. As a non-standard profile, permission had to be sought from the RSSB for the new wheelset design before it could be used during the testing and commissioning process.

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Automatic Power Control

What really makes a tram-train is its ability to adapt to different electrification and signalling systems. Sheffield’s Class 399 vehicles are dual- mode, allowing them to operate under the 750V DC catenary on the Supertram network and the national network’s standard 25kV AC OLE. The route to Rotherham will be electrified at 750V DC – a project due to be completed by the end of 2016 – but a dual-mode vehicle was seen as essential given plans to electrify the Midland Mainline to Sheffield by 2023.

The switching process is automated. An Automatic Power Control (APC) system, which uses magnets embedded in the ground outside of the rail, separates the two power supplies with a neutral section of track. As the vehicle travels over the first magnet it triggers the circuit breakers to open. The tram-train then coasts through the neutral section before detecting the new voltage and closing the circuit breakers. Although it is an automated process, there is a manual override which would allow the driver to close the circuit breaker if needed.

The signalling system, on the other hand, relies on a manual driver action. On the Supertram network, drivers will use the same visual signals and the vehicle identification system (VIS) employed by the conventional tram vehicles, but the new tram-trains are also fitted with TPWS and GSM-R equipment. Although the TPWS is active at all times, the driver will be required to activate the GSM-R as they pass onto the main line network. “It’s a bit of a reminder that they are now driving a train rather than a tram,” said Rob Carroll, major projects manager at Stagecoach Supertram.

Static testing has already started at Nunnery Depot. By next summer, the operator hopes to have received three of the vehicles from Vossloh’s factory in Valencia. Initially the tram-trains will be used to provide extra capacity in busy periods, with regular passenger services slated for early 2017.

Testing and validation of the wheel-rail interface began before Christmas and the first vehicle will begin testing on the tram network by the end of January. The 37-metre, bi-directional vehicles are made up of three articulated sections with three motor bogies and one trailer bogie. Each unit has a capacity for 88 seated and 150 standing passengers. Notable features include pneumatic suspension and rear-view camera displays in the driver’s cab.

Alongside the testing of the new vehicles, various infrastructure projects must be completed to allow tram-trains onto the network. Approval has now been given for Tinsley Chord – a 160-metre section of new track linking the two networks together. New stops are also being added at Meadowhall South and at Rotherham Parkgate, platforms are being extended at Rotherham Central station and the entire Supertram network is being re-profiled.

Over the Christmas period, the first of five LED integrated Lightweight Signals (iLS), which are being supplied by Unipart Dorman, was installed by Carillion on the line to Rotherham.

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Setting an example

The tram-train pilot will run for two years. The reliability and popularity of the service will be carefully scrutinised and its success could determine to what extent tram-train technology is adopted and embraced in this country.

Rob said that Sheffield’s tram-train project team was being approached by organisations around the UK. “Manchester has been very interested from the start, so we’re currently having quarterly meetings with Manchester just to relay what we’ve learned.

“We’ve now had a few meetings with Glasgow for the airport link, and South Wales are also interested.”

Glasgow is hoping to introduce a tram-train service between the city centre and Glasgow Airport. A tram-train is preferred over a conventional light rail system between Glasgow Central station and Paisley Gilmour Street. In South Wales, a mixed heavy and light rail network around Cardiff has been on the agenda for some time.

With aspirations to create a light rail connection between Nottingham and Derby, and with numerous tram extensions planned in Birmingham, no doubt other cities will watch Sheffield’s tram-train experiment with interest.