werk aan trambaan
In preparation for the real thing, a small trial demolition took place earlier. (Photo: M. van Bekkum)

Twenty years after the decision to extend tram line 19 across campus, it looks like it will actually happen in 2024. Only, the rails will be replaced starting 24 April. Why?

Lees in het Nederlands

“A tram line is urgently needed to reduce congestion in crowded car parks, on busy cycle paths and in overloaded buses,” says Dr Michaël Steenbergen who is involved in the design of the track as a vibration expert in rail infrastructure. According to Dick Huybens, Senior Project Manager Tramway at Campus Real Estate & Facility Management (CREFM), a tram is the ideal mode of transport for this purpose. It fits five times more people than a bus, and thanks to it having its own lane, traffic density hardly affects the timetable.

No wonder then that as early as 2001 it seemed like a good idea to extend the tram line from the station to and across the campus - a decision taken by the Delft city council in 2004.

But a tram would also cause vibrations on campus and magnetic fields that would disrupt research and experiments with highly sensitive equipment. Hence, the tram track that was constructed was given special features to reduce mechanical and electromagnetic disturbances. But because the tram was too heavy for the old Sebastiaans bridge (in Dutch), the bridge first had to be replaced and only buses drove over the Mekelweg tram track. So year after year passed and people cynically said "the tram will never come" Huybens recalls. He has refloated several stalled public transport projects, such as the line to Utrecht's Science Park. Now he is working to ensure that line 19 gets done. It is expected in early 2024 - 20 years after the municipal decision. Ordering a nuclear power plant goes faster. 

A brief history
What went wrong? “MRDH (Metropolitan Region Rotterdam The Hague, Eds.) wanted to use a different type of tram, but unfortunately the tram track on the Mekelweg was not suitable for it,” Huybens replied. Instead of The Hague's classic GTL-8 tram (in Dutch), the MRDH decided to schedule the more modern Regio Citadis (in Dutch). But its higher axle load (from 8 to 12 tonnes) and higher power consumption (1,200 instead of 700 amps) meant that the current tram tracks were unable to dampen vibrations and electromagnetic fields. So the existing tram track will be removed without a tram ever having run on it.

“Demolishing a tram track is no fun,” says Huybens. Noise, vibrations and dust clouds are inevitable. That is why CREFM has scheduled the work on public holidays and weekends that the campus is least crowded: 27, 29 and 30 April and then on 5, 6 and 7 May. The subsequent construction work will cause significantly less inconvenience and will last until the beginning of the next academic year. Until then, the bus will detour along Schoemakerstraat and Rotterdamseweg. After that, it will run on the tram line again, which by then will have been renewed.

‘It will be the most robust tram line in Europe’

Huybens expects the regular tram service to start running in the first quarter of 2024. The tram will then run up to X, turn left before the sports fields on the Van den Broekweg to the terminus just before Schoemakerstraat. There will be a break area for the tram crew and a crossover (‘tail track') to move the tram onto the other track. The tram will have a driver’s cabin at both ends so will not have to turn around. The AD newspaper (in Dutch) recently reported a delay in the felling permit for the trees on Van den Broekweg. Eelco de Vries, Communications Advisor at CREFMR, says that the latest planning has already accounted for this delay.  

“It will be the most robust tram line in Europe,” Huybens says of the construction. Once the old tramway has been removed, a composite 60 centimetre thick fibre-reinforced concrete structure will take its place on the existing bed of light volcanic rock. Weight is good because mass dampens vibrations. Unlike the existing track, the new track is specially designed to make cracks highly unlikely. The tram's large mass should roll over the rails as smoothly as possible, without vibrating and without bumping. 

Vibration expert Steenbergen (Faculty of Civil Engineering and Geosciences) explains how the track can shrink and expand with temperature without cracking. The concrete structure supporting the rails consists of 25 metre long sections. Each transition has a lower plate that carries the ends of the sections. A plate is also located halfway down the section where a notch has been made to mid-thickness, a crack leader. If a crack occurs, it will be at the notch, where an underplate will prevent subsidence. 

The top concrete layer acts as an uninterrupted 900 metre long expanse of concrete reinforced with synthetic fibres that gives it flexibility to prevent surface cracking. The material was discovered by Professor Erik Schlangen (CEGS faculty) in the US and developed there to reinforce bridges. Professor Schlangen became known for his self-healing concrete and asphalt. The rails are also surrounded by a thick rubber sleeve that absorbs noise and vibrations and provides electrical insulation (more on this later) with a 25 year warranty.

Sensors will be installed in the surrounding buildings to register vibrations and electromagnetic radiation from the tram. If these are higher than agreed, for example because the wheels are not perfectly round, the system registers the tram number.

Magnetic fields
Apart from vibrations, trams also cause variable magnetic fields. The overhead line is at 600 volts DC with respect to the rails. The current is capped at 1,000 amps on campus. One of the first to sound the alarm about this was Professor Pieter Kruit, an expert in electron microscopy. He calculated that a tram passing at 50 metres causes a field strength of about 300 nanotesla. Manufacturers of electron microscopes no longer guarantee resolution if the field exceeds 50 nanotesla and, for some high-resolution microscopes, no longer guarantee resolution if the field exceeds 20 nanotesla. It is therefore very important to reduce the magnetic fields of tram and lines, Kruit stated. Tesla is the unit of magnetic field strength: the magnetic field of the earth is about 0.00003 tesla, and of a refrigerator magnet about 0.005 tesla.

Kruit and Dick van Bekkum (EM Power Systems) designed an electromagnetic reduction system (EMRS) that was later implemented in Utrecht. It works like this. Normally, a large current loop is created between the overhead line and the rails when a tram is between them. The reduction system eliminates this by redirecting the current flow. With EMRS, the power supply of the overhead line runs through a thick conductor at the level of the tram rails. Each catenary mast has a feed wire to the catenary and back.

This means that a magnetic field is generated only in the section where the tram is located. That field is also addressed. As the overhead line has a greater resistance than the feeder wires, the pantograph (the contact point of the tram with the overhead line) draws most of the current from the shortest section of the overhead line because that is the path of least resistance. This creates two current loops on either side of the pantograph with an approximately equally strong magnetic field, but in opposite directions. The reduction in the magnetic field is about a factor of 10 at 50 metres. But because the Region Citadis draws more current and causes a larger magnetic field itself, Kruit and Van Bekkum were forced to further perfect their reduction system.

The new EMRS has not one but two reduction systems. The current through the pantograph (It) comes from two sides: (I1) from the left and (I2) from the right. The result is two approximately equally strong magnetic fields that run in opposite directions (according to the corkscrew rule) represented by the field symbols above the tram. That part is known. The second reduction system operates on the track sections between the tram and the feed station. The current feed is split into a large current (Iv) through a thick conductor 70 centimetres below the rails (d) and a smaller current (Ir) through the overhead line at 4.20 height (h) above the rails. This creates two current loops with a common discharge through the rails. The current strengths are set so that the product of current strength and the area of both current loops are equal and the magnetic fields cancel each other out at a distance. The current flow from the main underground conductor goes up and back at each overhead line mast. Behind the tram, no current flows through the conductors. To prevent stray currents and associated magnetic fields, it is important that the tram rails are isolated from the environment by a thick rubber sleeve. (Animation: Studio Stephan Timmers)

“You won‘t find a tram track like this anywhere in the world,” Huybens says. Because of its uniqueness, CREFM will organise a viewing day for public transport professionals on 1 June to introduce them to the home-made advanced engineering incorporated in the track. Huybens likes replacing cynicism with wonder, but he is realistic enough to know that once the tram runs, all the technical ingenuity will soon be forgotten, as will the long lead time. “If you don’t hear anyone talking about the tram anymore, then you have done your job well,” he says.