Friday, April 10, 2009

Sweden's Gröna Tåget (Green Train)


While the California bullet train system will run almost exclusively on brand-new, dedicated tracks, most other HSR systems (in the federal sense of the word) will require fast passenger trains to share track with heavy freight trains if dual tracking is to make economic sense. Sweden's national rail administration, Banverket, has essentially the same problem as many state DOTs in the US: large distances between cities, low population density, heavy freight trains (lumber, iron ore et al.) and on top of that, severe winter weather.

A particular problem is that high speed passenger trains (200+ km/h = 125+ mph in Europe) normally need tracks in very good state of repair to operate safely and with sufficient passenger comfort. Unfortunately, heavy freight trains with up to 25 metric tons axle load (cp. 17 for bullet trains) tend to chew up tracks pretty quickly. Without special train technology, the tracks would have to be repaired very frequently at great expense to maintain operational safety. Indeed, Banverket now wants to move toward a model in which train operators (from Sweden or other EU countries) pay trackage fees based on the amount of wear and tear they generate.

Safe, comfortable operation at 125mph on legacy tracks shared with heavy freight trains was achieved with the introduction in 1990 of rapid rail service based on the X2000 train, featuring a locomotive and up to 16 unpowered single-level cars (though 5 is typical). Designed in the 1980s by AdTranz, now a subsidiary of Bombardier, it features an array of technologies such as automatic train control, sensor-based active tilt control and an important innovation: soft bogies. In US terminology, bogies are called trucks; the standard configuration is two trucks of two rigid axles each underneath the car. What makes the X2000's bogies "soft" are special actuators that keep each individual axle perpendicular to the track, even in fairly tight corners. You can see them clearly in this video:

Note that Spanish manufacturer Talgo has long relied on a passive mechanism that links the single wheelset at the front of each short car with the body of the previous car to ensure wheels are always perpendicular to the rails, thus avoiding contact between the wheel flange and the inside of the rails. In addition to screeching, that causes wear and tear. The downside is that Talgo trains are by definition articulated trainsets that cannot easily be reconfigured into longer or shorter consists.

The X2000 trains are complex and therefore expensive to buy and maintain. However, that must be weighed against the savings achieved by using legacy instead of brand-new track. Passenger volume went up dramatically with the new service, as did public willingness to invest in major rail transportation upgrades, e.g. the Øresund bridge/tunnel to Denmark. They were also tested by Amtrak, along with first-generation ICE trains from Germany. In the end, the Acela Express contract went to Bombardier. Late in the development of the design, FRA insisted on ludicrous crash compatibility requirements that severely compromised the mean time between failure (MTBF) of the active tilt and other subsystems.

A few years ago, Banverket launched a new public-private research program called Gröna Tåget (Green Train) to build on the success of the X2000. Partners include top Swedish engineering universities and Bombardier. Key objectives include:

  • improved reliability in severe winter conditions
  • increasing top speed in commercial operation to at least 250km/h = 155mph
  • exploiting the generous track spacing with five instead of four seats abreast
  • improved passenger comfort in corners
  • reduced wear and tear on the infrastructure
  • lower electricity consumption
  • no increase in noise over the X2000
The project overview states that the new, higher top speed will only be achievable on upgraded or brand-new track sections. That's because the signaling on the legacy tracks imposes a limit of around 125mph. In addition, the popularity of the X2000 has introduced capacity problems. The high cost of enhanced rail infrastructure in rural areas makes more sense if it can support passenger trains running at higher speeds.

The key innovation expected from the research program is active lateral suspension (ALS), which will reduce wear and tear on the rails and also improve passenger comfort in curves. Most other upgrades, including electric multiple unit (EMU) traction based on permanent magnet synchronous motor (PMSM) technology, triple brake system, wide car bodies etc. are already present in Japanese, German and/or French train designs. What sets the Swedish effort apart is the ambition to make all of that work very reliably in arctic winter conditions - a task that off-the shelf HSR train designs on the European market aren't quite up to.

In the summer of 2008, the Gröna Tåget test train set a new Swedish speed record of 303 km/h on a section of straight legacy track originally designed for 200 km/h. While that's less than modern bullet trains can achieve on dedicated tracks, it represents a major technical milestone for rapid rail. In spite of the inevitably high cost of train designs that will be derived from this R&D platform, they could prove a good fit for HSR in North America - especially for the frigid winters of the Midwest, Northeast and Canada. Interested readers may want to check out the technical documents.

In California, HSR train designs that get the most out of legacy freight track could make a lot of sense on the Amtrak Pacific Surfliner and Capitol Corridor routes, perhaps others as well. The idea would be to spend public money on adding a second track and upgraded signaling, while the freight operator upgrades his existing track. Then, both share both tracks via mutual trackage agreements or else, the infrastructure becomes the property of a public-private partnership.

However, it is imperative that FRA develop a regulatory path toward mixed traffic, i.e. allowing slow, heavy freight trains and fast, light passenger trains to share dual track alignments via appropriate signaling upgrades, timetables and bypass sections. Rapid rail will require close relationships with freight rail operators and substantially more public money that the US has traditionally spent on passenger rail, but it could make electrification and high speeds a reality for many existing rail rights of way in the designated federal corridors.


arcady said...

If only the FRA had allowed the X-2000 to continue to operate beyond the demonstration period! Life would have been so much easier for Amtrak and the passengers on the NEC.

Rafael said...

@ arcady -

last month, the Obama administration has nominated a new FRA administrator, Joe Szabo

If confirmed, he will bring to the job a lot of experience in railroad operations. His current job is Illinois state director of the United Transportation Union and he understands the number of additional union jobs that would be created by upgrading and expanding intercity passenger rail nationwide.

Nevertheless, I suspect it will be some time before rules enabling that expansion will be drafted. The freight operators do not yet see that as being in their interest and will therefore try to use their influence in Congress to avoid rule changes that could prove expensive for them.

That's why I think it would make a lot of sense to consider the freight operators' business model in the plans and create a combination of transportation policy and safety rules for rapid rail operations based on mixed traffic.

Note that there are plenty of rail issues related to freight alone, e.g. the introduction of interoperable PTC as mandated by HR 2095, level boarding platforms and, speeding up the passage of rail freight through the transcontinental transfer points roughly along the Mississippi river, especially Chicago.

Alon Levy said...


I can't really see it. What should I be looking for?

Rafael said...

@ arcady -

the radial steering actuators are the hydraulic struts mounted at an angle on the outside of the trucks.

The objective of soft bogies is to create a small angle between the two axles on each truck as the train runs through a tight corner. That's why only one axle per truck is needed.

Anonymous said...

it's a nice train - but every time I'm ridden it I've become terribly sea-sick. As the train tilts, one doesn't feel the lean, but the damn horizon keeps shooting up and down. I've not experienced this on Acela - but that doesn't run nearly as fast as the Swedish Railway.

Rafael said...

@ anon @ 3:14pm -

motion sickness is one of the problems associated with a mismatch between visual and acceleration cues picked up in the labyrinth. The new active lateral suspension is supposed to address precisely this problem.

There aren't a whole lot of heavy freight trains that run in the NEC, so perhaps the tracks there are in better shape. The FRA-imposed greater mass of the superstructure certainly dampens the lateral vibrations better, but given modern control systems technology, that's a really inelegant brute-force approach.

In any event, smooth running at high speed on tracks in so-so shape along a twisty alignment is hard to achieve.

TomW said...

@ anon @ 3:14pm:
What's happenign is that the tilt mechanism is working too well - so the lateral G forces are exactly conceleld out, and your brain gets confused by the visual cues.
British Rail foudn this when they develoepd the world's first tilting train (the APT), which is why the 'Penodlinos' in use in Britain today (and descended form theAPT via Italy) still leave a bit of lateral G force remaining.

gardebring said...

Just thought I would share a video of the 303km/h record for the green train in Sweden:

I really want these to go into operation soon...

gate valves said...

nice blog. what a great looking train.