Rolling stock manufacturers are studying the potential for reducing the weight of rolling stock, with a view to cutting energy consumption and life-cycle costs. Experience from Japan suggests that taking a strategic view offers long-term benefits

Prof Mark Robinson is Director of NewRail, the Centre for Railway Research at the University of Newcastle upon Tyne. Hiroshi Nomoto is Manager of the Rolling Stock Development Group at JR East's Advanced Railway System Research Centre

ENERGY COSTS for rail operators are predicted to rise sharply over the next few years, focusing attention on ways to improve operating efficiency by reducing the weight of rolling stock. In recent years this has risen relentlessly, reflecting higher crashworthiness standards, heavier and power-hungry auxiliary equipment, and disabled accessibility requirements, amongst other factors.

In the UK, a drive to cut the mass of future rail vehicles is being led by Rebeka Sellick, ATOC Technical Director and Chairman of the Vehicle/Vehicle System Interface Committee, and Richard Gostling, Chairman of the Advisory Group on Rail Research & Innovations.

Setting a target of a 30% reduction in vehicle mass, Sellick and Gostling organised a seminar in November 2005 to come to a collective understanding of the constraints, opportunities and trade-offs that should be considered. This concluded that lessons could be learnt from the strategic approach adopted by East Japan Railway, which has seen the mass of commuter EMUs cut by almost 50% over the past 50 years.

Commuter operations account for the vast majority of passengers handled by JR East, which includes the Tokyo metropolitan region within its operating area. JR East carries 16 million passengers a day, which is almost six times as many as the entire UK rail network. This is reflected in the makeup of rolling stock fleet; commuter EMUs account for two-thirds of the 12000-car total, compared with 1100 Shinkansen vehicles.

Evolution strategy

Fig 1 shows the evolution of Tokyo suburban EMUs. During the 1950s the trains were relatively heavy, until design optimisation and a change of traction motor in 1958 saved about 10 tonnes. But the mass saving then went into reverse - as was common elsewhere in the world - by improved passenger comfort including air conditioning.

Significant weight saving came in the 1980s with a move to stainless steel bodyshells and the use of finite element analysis to optimise mass reduction for the Series 205.

After the breakup of JNR, the drive for mass reduction continued at JR East. The goal for the next generation of EMUs (Series 209) was to reduce life-cycle costs - what JR East described as half-weight, half-life, half-cost. Development began with the construction by the railway's own workshops of three prototype Series 901 trains (now designated Series 209.900). These were fitted with different components for comparative tests to validate the most appropriate technologies for the series version.

Amongst the components to be evaluated were the main circuit inverter, motor, bodyshell, door mechanism, air conditioning, master controller and interior design. After all of the components had been verified, JR East was able to fix the specification for volume production of the Series 209 fleet.

This process achieved a mass reduction of 122 tonnes over a 10-car trainset, representing a saving of 34% compared with the Series 103 developed in JNR days. There was a saving of around 30 tonnes in the body structure, 35 tonnes in the bogies and about 20 tonnes in the main traction equipment.

By adopting competitive tendering, the initial cost of the vehicles was reduced by 30%, despite the extra costs of improved passenger facilities and passenger information systems. The mass reduction, regenerative braking and an improved design of asynchronous traction motor all contributed to an overall reduction of 53% in energy consumption. Further savings were achieved in maintenance costs through better initial design and the introduction of new maintenance processes.

Series 209 sets were first introduced on the Keihin Tohoku Line from 1993, followed by the Series 209.500 cars on the cross-city Sobu Line. But seven years after the first introduction of Series 209, JR East switched to another new generation of suburban EMU, the Series E231, which is still in production.

The biggest step-change with Series E231 was the move from GTO to IGBT traction controls and introduction of advanced microprocessor-based train control systems. This versatile technology allows the trains to meet different performance specifications for inner-urban commuting and outer-suburban operations with the same traction package.

The first Series E231 trainsets were put into service on the Jyouban Line in 2001, and on the busy Yamanote Loop in the following year. More recently, a suburban version of the Series E231 was introduced to the Tokaido Line during the 2005 financial year, bringing the total number of new-generation EMU vehicles introduced by JR East to more than 4000 cars.

International comparison

Table I compares the most recent JR East commuter EMUs with two equivalent metro trainsets recently put into service in European cities.

An immediate difference is that the standard length of a Japanese trainset is 200m, formed of 10 cars 20m long. The European trains are both six-car formations totalling about 110m. To enable a better comparison, we determined the total number of passengers and compared the vehicle mass per passenger.

In Japan the floor capacity is defined as 0·3m2 per person. Thus 100% capacity is when all seats are occupied and the density of floor passengers is at this level, with approximately three passengers standing in a 1m x 1m square. When there are six people per m2, as in the table, the standing area is considered to be 180% congested. The Japanese industry standard for maximum standing load is three times the defined level (10 passengers/m2). With the seating capacity unchanged, the crush load is therefore around 250% of the nominal capacity.

The Wien V-Car compares favourably with the Japanese designs. Madrid's Series 9000 is both shorter and heavier. This is mainly due to heavier external doors and bogies, although extra mass comes from the design of the seats, cab, passenger information and communication systems, and the on-vehicle surveillance equipment. Another issue is the lower number of standing passengers which is caused by four main factors:

  • The vehicle is relatively narrow, with only 1500mm of gangway width between the longitudinal seats;
  • The seats are large and comfortable, which reduces the amount of floor space available for standees;
  • The provision for disabled passengers also reduces available floor space,
  • The inter-car gangway is also relatively narrow at 1350mm.

We suspect that this vehicle was designed to suit the capacity determined by the operator for the routes it will serve. When this was easily achievable the designer was able to use the free space to enhance passenger comfort through improved seating rather than provide unnecessary extra capacity.

Material substitution

The Japanese experience demonstrates that there are cost and energy benefits associated with lighter weight. We might reasonably ask why there has not been a greater use of lightweight materials, such as composites, in European rail vehicles. JR East uses composite materials for interior panels to cut manufacturing costs.

There are some technical issues that clearly need to be addressed, including the additional complexity of designing and manufacturing with composites. This would apply particularly to their use for body structures. But are there also more general barriers that need to be overcome by the European rail industry?

One initiative that is currently addressing this issue is the EU-funded Modurban project. Within this programme there is a specific team working on 'Removing constraints on the use of lightweight materials'. This team includes Alstom, Ansaldobreda, Bombardier, Siemens and Roma public transport authority ATAC, together with NewRail.

The project is examining ways to make it easier for designers to evaluate lightweight materials alongside traditional techniques, and will highlight regulatory or cultural hurdles that need to be overcome. As a starting point, the team has examined the mass distribution of a typical state-of-the-art metro vehicle (Fig 2). This shows clearly that five elements represent 75% to 80% of a vehicle's tare mass: bogies (40%), bodyshell (20%), interior fittings (10%), heating, ventilation and air-conditioning (5%) and the external doors (5%).

At this stage, it is important to ask what proportion of a vehicle's tare mass can potentially be influenced by material substitution. Some categories, such as vehicle interiors, are readily amenable to the use of composites, whilst others like HVAC are less-likely candidates.

Table II provides a rough-and-ready sort to concentrate efforts on the categories offering the greatest benefits. Correlating this against the masses listed in Fig 2 suggests that around 80% of a vehicle's tare mass can potentially be influenced by material substitutions.

We recognise that this crude analysis has a number of limitations, and there will be exceptions within each category. There may also be technical, economic, or regulatory barriers preventing the introduction of lightweight materials in some areas, for example fire performance.

Lightweight materials such as fibre-reinforced polymers may already be used for certain interior components, which could make it difficult to achieve further significant weight reductions. However, there may be opportunities for functional integration through the use of lightweight materials. For example, foam-cored sandwich materials may be inherently thermally insulating, and may contain ducting for electrical systems or air-conditioning.

We envisage that there may be opportunities for lightweight design using new materials. A properly designed lightweight composite component could look very different to a metallic alternative, rather than simply being a like-for-like 'black metal' replacement. And our simplified analysis does not consider at this stage the potential knock-on effects. For example, a lighter door might require a smaller and lighter motor to operate it.

It should be noted that all of these figures relate to the tare weight of the vehicle, and we should not forget the additional operational weight including the passengers. The total weight of a fully-loaded metro trainset is around 100 to 150 tonnes greater than the tare weight. And of course this extra loading cannot be influenced by material substitutions!

Even where components are not amenable to material substitution, they need to be reviewed in terms of their systems performance. For example, the latest communications technology can reduce dramatically the quantity, and weight, of cables and connectors. At JR East the Series E231 has 80% less cabling than Series 209.

Another focus for weight saving in Japan at present is a reduction in the number of bogies. As these account for around 40% of total vehicle mass, there are potentially some big savings to be achieved through articulation (Fig 3).

Start with a strategy

JR East's work demonstrates the benefits of having a clear strategy for mass reduction and setting targets for each stage of development. Comparison of prototype trains gives the opportunity to use a systems engineering approach to revise the entire vehicle, including electrical components. In addition, Japan does not have the same severe regulations on the strength of vehicle body structures that we have in Europe.

This article has mainly focused on materials substitutions, because that is the area where NewRail is currently working. However we are extremely well aware that a systems review can also reduce vehicle mass significantly. In the case of Series 209, 20 tonnes was saved by simply changing the main traction control circuits.

And it is important to remember that rail vehicles are just one part of a larger system with many components. Each component is intimately linked with others, so taking a systems approach to mass reduction has proven to have a significant effect.

It is clear from our work so far that strategies can be put in place to prevent trains getting heavier. There are major benefits from lighter vehicles which can be exploited in terms of energy savings, cost savings, infrastructure management and route capacity increases. However, it is essential to exercise caution when making comparisons between modes.

There are a number of technical and cultural barriers to be overcome if lightweight materials are to be specified more widely within the rail industry. Vehicle designers will need tools to compare different materials and functional implementation on the basis of life-cycle costs. In terms of cost, it is also important to consider the number of components and the potential for simplifying the maintenance regime.

  • CAPTION: TOP: JR East's Series E231 EMUs operate several Tokyo suburban routes
  • CAPTION: Ansaldobreda is currently building 52 six-car Series 9000 trainsets for the Madrid metro, with an option for a further 237 vehicles
  • CAPTION: Developed using the Siemens MoMo modular concept, the V-Car is the latest generation of metro stock for the Wien U-Bahn
  • Fig 1. Mass reduction achieved through the evolution of Japanese commuter EMUs
  • Fig 2. Breakdown of tare mass for a typical metro vehicle Source:Modurban
  • Fig 3. Articulation was tested by JR East on the Advanced Commuter Train prototype and the results will be verified in comercial service using the Series E331 trains (p272)

Table I. Comparison of Japanese and European EMU designs

Type V car 9000 209 209.500 E231

City Wien Madrid Tokyo Tokyo Tokyo

Manufacturer Siemens Ansaldo- Kawasaki, Tokyu Car, JR East breda

Train formation * C+S+S+ M+T+S+ 4M6T 4M6T 4M6T S+S+C S+T+M

Total length m 111·2 108·3 200·0 200·0 200·0

Car width mm 2850 2808 2800 2950 2950

Tare weight (tonnes) 162·6 193·0 241·0 255·0 256·0

Number of seats 260 178 522 518 518

Number of standees (at 6/m2) 1360 1094 1832 1926 1926

Total train capacity 1620 1272 2354 2444 2444

Weight per passenger kg 100·37 151·73 102·38 104·34 104·75

M = driving motor car, S= non-driving motor car, C= driving trailer, T = trailer

Table II. Vehicle elements amenable to mass reduction through material substitutions

Suitable Unsuitable

Bodyshell Power/Propulsion

Windows Auxiliary power supply

Exterior attachments Brake system &

Gangway pneumatics

Bogies Passenger information Passenger interior systems

Communication & Harnessing, cables & surveillance systems connectors

Seats Heating, ventilation & Cab interior and cabinets air-conditioning

External doors Others


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