INTRO: Shoehorning power equipment and auxiliaries into the limited roof space available above the bogies on an EMU car with upper and lower saloons between vestibules was first achieved in Sydney. Now Europe is beginning to follow suit

BYLINE: John Dunn *

Transit Design Pty Ltd

GROWING CONGESTION on urban roads is forcing many commuter operators to find ways of providing more seats without building extra tracks, lengthening station platforms or resignalling to reduce headways. Or perhaps more capacity is demanded after exhausting some or all of these options.

One obvious method being adopted ever more widely is double-deck coaches. Apart from the gallery cars introduced from the 1950s in North America, where ample height is available, modern commuter stock has a depressed centre between the bogies permitting full width and full height saloons on two decks.

Entry is by stairs from large vestibules at opposite ends, where passengers can assemble before alighting, or crowd in quickly when boarding. There is normally space for a few seats outboard of the vestibules, or it may be set aside for standees, wheelchairs or toilets.

Double-deck stock has been around in one form or another for well over a century. But long after EMUs replaced single-deck loco-hauled coaches in electrified territory, many double-deck operators still use a locomotive or dedicated power car operating in push-pull mode. Such trains were introduced in Paris during the 1930s.

Sydney led the way

Double-deck EMU development commenced modestly in 1964, when New South Wales Government Railways first introduced 20m long trailer cars into the large fleet of single-deck units serving Sydney’s 1·5 kV DC suburban network. The objective was to raise capacity through stations designed for two 4-car units, each just over 80m long.

This new design with full-height, full-width saloons on both decks increased the seating capacity of the trailers by 47%. Though shorter, their design was based largely on the 1930s Paris cars.

At that stage, NSWGR engineers gave little thought to double-deck power cars because the traction control equipment, batteries, air compressors and other auxiliary gear were slung from the underframe between the bogies. In view of the size and mass of equipment available at the time, it appeared quite unrealistic.

Nevertheless, the success of the trailer cars led to the commissioning in 1968 of prototype double-deck power cars from four manufacturers to test the concept. The cars would be based on the design of the existing trailers, and as much as possible of the traction and auxiliary equipment would be housed in the roof above the vestibules. Only very heavy items such as air compressors, motor-alternators and batteries would remain at underframe level.

The severe restrictions on available space in a 20m long body, allied to mass and centre of gravity constraints, forced equipment suppliers into a good deal of lateral thinking. Major items of equipment had to be smaller, lighter and more tightly packaged.

In those days, traction power was regulated by camshaft switching of naturally-ventilated resistors, neither of which could easily be reduced in size. Nevertheless, both were shoehorned into the roof cavity above the ceiling of the leading end saloon and doorway vestibule. Other equipment, including the pantograph, was housed in the rear end of the roof.

The outcome was four double-deck power cars that basically achieved the desired goal of 50% more seating with a minimal loss of car interior space to equipment.

NSWGR subsequently called tenders for stainless steel all double-deck EMUs with 24m bodies for interurban services. The added feature was air-conditioning, posing another huge challenge to the car designers and the equipment suppliers. Once again, new thinking was needed to accommodate all the equipment, air ducts and cabling without compromising passenger seating space.

Unlike their suburban counterparts, equipment was at first shared between power cars and trailers. Subsequent versions (above) had all traction equipment located on the power car.

This was also the first time that complete equipment packages were tailored to suit the space and the shape of the roof bays. For example, roof-mounted air-conditioning modules were self-contained with their exterior skin conforming to the outer shape of the car (below).

When these trains entered service in 1970 they were the first of their type in the world, and became the benchmark for subsequent variations in NSW as well as those developed in other countries.

In time, chopper-controlled propulsion replaced the camshaft units on both suburban and interurban double-deckers, although no attempt was made to rationalise the design to gain more passenger capacity from these newer, more compact components.

Not until the advent of the Tangara EMUs in the mid-1990s was a completely new concept launched. Roof-mounted auxiliary and traction control modules were spread between power cars and trailers, each bay being fairly tightly packaged (above right). The 20m Tangara cars did not increase seating capacity, but they did provide larger vestibules and entrance doors, plus better stairway access to both decks.

Designers of the latest 4GT double-deck EMUs for Sydney (RG 3.99 p161) have tried to exploit the reduced size of IGBTs and AC motors as well as power bogies which have no overhanging outer headstocks. As a result, these eight-car units (below left) will have slightly increased seating capacity at 904 compared to 872 in the Tangaras.

Further rationalisation of the concept and layout of these trains will doubtless achieve even greater gains, probably breaching the target of 1000 seats within the 163m train length.

Problems in Europe

For European designers, packaging auxiliary and traction control equipment into a double-deck power car is significantly more difficult than it was for Sydney. Cars are typically 26 to 27m long, and consequently heavier. High AC voltages pose much more taxing electrical clearance problems, and transformers are very awkward to accommodate.

Nevertheless, a number of railways in Europe are introducing double-deck EMUs into commuter and interurban service. It is instructive to examine the different approaches being adopted.

SNCF introduced the first Type Z2N double-deck EMU power cars in 1984 for Line C of the Paris RER. Due to the need for high speeds, high acceleration and dual-voltage operation, bulky equipment had to be accommodated within the power car end saloons, limiting seating capacity.

Not until 1996 did the Type MI2N appear for use initially on Line E, and later on Line A. With short station dwell times at a premium, all cars have three vestibules with pairs of upper and lower saloons between them (RG 3.96 p132). Thanks to advances in power equipment, space taken up by equipment lockers is much reduced.

There is a similar history in Germany, where large fleets of double-deck push-pull trains serve major cities and new EMU versions are planned. The prototype - displayed in 1998 at InnoTrans in Berlin - had two driving power cars and an intermediate trailer. However, most of the equipment is in large cubicles within the power cars, and roof space appears under-utilised.

Rationalising the layout would produce a much higher seating capacity than is currently being achieved. Packaging equipment in roof bays above the end saloons and selecting components that can be adapted specifically to the double-deck concept would be essential. It might also mean distributing equipment between the power cars and the trailer.

With a high-voltage AC supply, there remains the question of where to house the transformer. To optimise this choice, the car designer must be free to select the product best suited to the space available. This may not be possible where cars are being designed by an integrated supplier determined to use his own standardised products.

A similar criticism might be applied to the TAF double-deck EMUs recently introduced by Italian State Railways (now Trenitalia), especially as they are 3 kV DC and not high voltage. Very large equipment bays take up the leading end of the power cars (above right), and the roof space above the end saloons does not appear to be fully exploited.

The purpose of going double-deck is to maximise seating capacity. With little more than 80 seats in the 25·9m power car (albeit with a disabled-accessible toilet), the question arises as to whether this is an efficient design when almost as many seats can be accommodated in a single-deck car of a similar length with similar facilities.

Czech Railways introduced double-deck EMUs in the 1990s, but the power cars did not have any passenger seating on the top deck (centre). The full length of the upper section of the car is taken up with equipment, including two pantographs. More recent EMUs have full double-deck saloons on both decks of the power car (p110).

Netherlands Railways introduced double-deck commuter EMUs in 1995, adding power cars to former push-pull sets. Like the German cars, the bogie centres are spaced to a maximum of 20m with short overhangs to the car ends. Hence there is not much space available in the roof at the car ends, and it is mainly occupied by air-conditioning modules. Two sizeable equipment bays are therefore located on the lower deck of the power cars.

NS also operates a fleet of double-deck inter-regional EMUs (RG 5.94 p285).

French National Railways has just ordered a second generation of double-deck EMUs for regional services (RG 12.00 p788). These will be based on Alstom’s Coradia Duplex concept which was initially developed as an inter-city push-pull vehicle for SNCB in Belgium (RG 11.99 p709).

Intended for dual-system operation on 1·5 kV DC and 25 kV AC, (and potentially 3 kV and 15 kV 162/3Hz as well), the TER-2N NG sets (right) will have distributed power. IGBT-based Onix drives will feed two three-phase motors of 390 kW on one bogie of each vehicle. One driving car will accommodate the wheelchair-accessible toilet on the lower deck, and the other will have first-class seating at mid-level behind the cab. A two-car unit will seat 22 first and 171 second-class passengers, rising to 58 first and 446 second in a five-car formation.

Japan squeezed on height

Japan has been using double-deck commuter stock for many decades. EMU sets on the Kintetsu Railway have no seats on the lower decks of their twin-pantographed power cars, this space being entirely occupied by equipment.

A more recent design was introduced by JR East in the mid-1990s. Although 1067mm gauge and narrower in body width than the Sydney cars, the arrangement of these 10-car stainless-steel prototypes followed the Australian concept with full width, full height saloons on both decks, and packaged air-conditioning units in the roof above both vestibules.

However, although these cars are about the same length as those in Sydney, they are not as high. Probably for this reason, the Japanese designers elected not to house any of the main propulsion equipment and auxiliary equipment in the roof. Instead, the ’lower’ bays of the two driving cars are used as full-length equipment bays. In fact, they have conventional underframes and no drop gondola as on the trailers. Like the earlier Kintetsu power cars, passengers are accommodated on the upper deck only.

Space issues

Up until the latest contract, all of Sydney’s double-deck power bogies had outboard headstocks because the traction motors were too large to permit inboard disc brakes. Thus the length of the bogies impacted on the length of the lower deck gondola, and then on passenger seating on both upper and lower decks. This restriction has generally been true of all double-deck power cars worldwide.

With the advent of much smaller AC traction motors, power bogies with no overhang beyond the wheels are possible. The way is therefore open for designers to use gondola lengths on the power cars commensurate with those on trailer cars.

When the first production double-deck EMU power cars were being designed for Sydney in the late 1960s, it was hard to persuade equipment suppliers to think in terms of packaging their products to suit the unique requirements of double-deckers. It was the Japanese who agreed to come up with modules that conformed to the car roof shape, and thus fitted within the roof equipment bays.

Had they not done so, it is unlikely that Sydney’s full double-deck EMUs would have been the success that they have been.

In three decades the problem has come full circle. Nowadays, equipment suppliers are as reluctant as ever to produce non-standard modules. Although their products are smaller and their packages more compact, they tend to standardise for underframe mounting on single-deck cars.

So for double-deck car designers, the gains made through reduction in the sizes of individual components are being thwarted by the ever-pressing desire for traction package manufacturers to standardise their products, thus achieving economies of scale in production.

It is the length of the saloons between the bogies that largely determines the seating capacity of a double-decker. Does this mean designers ought to revisit the concept of articulated double-deck cars?

The significant reduction in equipment sizes in recent years, together with the development of ultra-lightweight structures and more compact bogies, should enable designers to create an efficient double-deck articulated EMU. Axleload then becomes the primary limiting factor, if three-axle bogies are to be avoided. Even though the cars might be shorter than usual, such a train would maximise seating capacity within the limits of existing platform lengths.

Here in Sydney, new interurban double-deckers will be needed in this decade. Their design features will be quite different to those that made headlines 30 years ago. The new concept would make full use of all double-deck car developments, conceptual innovations and technological advances that have taken place in the past three decades around the world.

Thus it is not inconceivable that they would have 30 to 35% more seating as well as being faster, quieter, more luxurious - and maybe dual-voltage to accommodate possible future 25 kV electrification for projects on the East Coast.

* John Dunn is an independent railway consultant specialising in the concept design of passenger rolling stock

CAPTION: Double-deck interurban EMUs in New South Wales were the first in the world to have traction and air-conditioning modules in the roof over the end vestibules. This is the second series

CAPTION: A typical self-contained air-conditioning pack for the Sydney interurbans. The pack’s outer skin conforms to the car roof profile

CAPTION: Sydney’s four-car Tangara air-conditioned suburban double-deck EMUs (above) also have roof-mounted equipment modules (right)

CAPTION: Full size mock-up of Sydney’s 4GT ’Millennium’ double-deck suburban EMUs

CAPTION: Above left: Bombardier’s prototype three-car double-deck EMU for German Railway at InnoTrans 98

Above: Trenitalia is buying 80 double-deck TAF EMUs for suburban operations in Milano and Roma; a train from Civitavecchia calls at Roma Trastavere

Photo: Quintus Vosman

CAPTION: Centre: Czech Railway’s first four-car double-deck EMUs carried passengers on the bottom deck only of the power cars


Below: Artist’s impression of a French National Railways’ four-car TER-2N NG at Lille Flandres

Alstom/MBD Design

CAPTION: The driving power car of a JR East Series 215 double-deck EMU has passenger accommodation on the top deck only

Double-deck power cars expand EMU capacity

Shoehorning traction equipment and auxiliaries into the limited roof space available on an EMU power car with upper and lower saloons between vestibules above the bogies was first achieved in Sydney. Now Europe is striving to maximise seating capacity by designing power cars with minimal loss of revenue earning space. One way is to distribute equipment between power cars and trailers to meet weight limits on 26m long cars, but it needs to be carefully packaged so as to fit the curved roof profile.

Les motrices à deux niveaux augmentent la capacité des automotrices électriques

Rentrer au chausse-pied les équipements de traction et les auxiliaires dans le peu de place disponible sur le toit d’une automotrice électrique, avec ses compartiments voyageurs situés entre les plateformes d’accès, au dessus des bogies: voilà l’opération qui a été réalisée pour la première fois à Sydney. Désormais, l’Europe s’efforce de rechercher le maximum de capacité en places assises en concevant des automotrices qui permettent de limiter au minimum les pertes de recettes. Une solution consiste à répartir les équipements parmi les motrices et les remorques, afin de rester dans les limites de charge imposées pour des voitures de 26m, mais il faut alors soigneusement loger ces équipements pour qu’ils puissent s’inscrire dans la courbe des toitures

Doppelstock-Triebwagen erh