Scott McIntosh explores some of the issues surrounding the great tramway gauge debate,
while Richard Buckley considers a few of the seemingly more bizarre gauges and the reasons behind their adoption.The subject of an ‘optimum’ gauge for railed transport systems is endlessly fascinating and debate of the issue can while away many a long evening for amateurs and rail professionals alike. The great George Stephenson seems to have given the matter little thought, simply building locomotives to match the crude colliery railways that already existed. His son Robert, with a wider technical knowledge and considerable experience in building locomotives, publicly stated that it would be better if a gauge ‘about six inches wider’ [15cm] could be adopted to allow greater space for locomotive machinery. However, he also acknowledged that it was probably too late and that the economic solution was not to seek the best gauge but to accept the commonest.
Broad gauges were said to offer greater stability, or allow for more powerful locomotives. Brunel’s ultimate broad gauge (2140mm/7ft ¼in) was originally adopted to allow the carriage body to fit inside large wheels, offering reduced rolling resistance and a low centre of gravity – an obsession amongst early railway designers. Interestingly, only one design of broad gauge coach adopted the ‘body between the wheels’ design, all the others used a more conventional ‘body on top’ layout, albeit with some wheel projections through the floor.
Dispelling a few myths
Narrow gauges were said to offer savings in construction costs and to allow sharper curves to be used. However, a little thought will show that placing the rails closer together will effect only minimal savings in the cost of sleepers; the real saving comes in having a narrower loading gauge, not a narrower track gauge, but this comes with a reduction in the carrying capacity of each vehicle. Ironically, metre and ‘Cape Gauge’ (1067mm/3ft 6in) colonial railways often have generous loading gauges; the South African rail network employs Cape Gauge and has a maximum width of 3048mm (10ft) and a maximum height of 3962mm (13ft), greater than the standard British loading gauge.
The curve radius question is more interesting; previous TAUT articles have discussed the problems of fixed-axle vehicles going round sharp curves and it would be safe to say that if one has two steel wheels fixed on an axle and very sharp curves then a narrower gauge will be marginally beneficial. However, it must be remembered that some first-generation tramways combined standard gauge alignments and curves of under 11m (35ft). Toronto still combines 12m (39ft) curves with its peculiar 1473mm (4ft 10in) gauge track. Of course these curving problems can be mitigated if the tramcar is fitted with individually-controlled wheel motors, these can eliminate skip-slip on curves entirely.
It has been claimed that lateral oscillation of rail vehicles is a major concern on narrow or metre gauge track, but these issues could be addressed by modifying the track panel resistance. These difficulties are unlikely to arise at the lower maximum speeds of tramways, however. The Queensland Railways in Australia have shown that a well-aligned Cape Gauge track can carry trains operating at up to 170km/h (105mph) and tramway slab track already offers greater lateral resistance than ballasted heavy rail track. Nor does a narrower gauge unduly restrict vehicle height or width. Hong Kong (and in an earlier era Birmingham, UK) show that high-capacity double-deck cars can be successfully operated on 1067mm gauge track and in Trondheim, Norway’s metre gauge Ggråkallbanen has successfully operated 2.65m-wide light rail cars for many years.
There are fears that narrow gauge low-floor cars might be more difficult to construct, with unacceptably narrow gangways and constraints on traction motor size. However, German cities such as Frankfurt an der Oder and Jena have been running Adtranz GT6M cars, with longitudinal, flank-mounted motors since the 1990s. The later Variotram (and Variobahn) is available in metre gauge versions with significant orders delivered to Mannheim, Helsinki and Bochum. This variant has hub motors on all wheels, thus eliminating the need for axles entirely. Siemens also reports that a significant proportion of its Combino low-floor variants have been built for metre gauge systems.
A new entrant to the rolling stock market is the Ukrainian concern Elektotrans – it is currently delivering 100% low-floor trams to the metre gauge network in Lviv (see TAUT 935). In February 2016 the Russian car builder PK Transportnye Systemy presented a prototype that it is building for Yevpatoria. Its 2.3m-wide Varyah (which bears a striking resemblance to the Škoda/United Streetcar vehicle) is designed for metre gauge networks.
Metre gauge is still growing
There seems to be a general consensus that no new systems should be built to any gauge other than 1435mm, yet there are three new-build tramways in Bilbao, Valencia in Spain and in Eskiehir, Turkey, that are metre gauge.
At one time there was a drive to convert legacy systems to standard gauge when they were modernised; this was done in Stuttgart, Essen and Chemitz in Germany. Sofia, Bulgaria, began a gauge conversion programme in the late 1980s, but this was halted after its second standard gauge line was completed. It is difficult to see what advantage was gained by this work as cars of similar size and performance could have been provided on metre gauge track. In other cases it is sensible to seek gauge standardisation across a network to allow integration of services and maintenance.
This has been the reason for many conversions in Germany, which makes the decision in Toronto to make the Transit City LRT lines a different gauge to the TTC streetcar and metro lines seem even more bizarre. Stadtwerke Ulm has ordered 12 Avenio M low-floor trams as part of a project to expand the German city’s metre gauge tram network with the addition of a new line 2. The planned 10.5km (6.5-mile) route will have 20 stops and will share tracks with line 1 for 1.2km (0.75 miles) in the city centre when it opens in 2018. Interestingly, the project budget cost is approximately EUR192m (less than EUR21m/km), but I suspect that this low cost is due to German efficiency and the employment of standard contracts rather than any inherent economy in metre gauge.
What about going wider?
Tramways built with a broader gauge may offer some advantages, particularly where 100% low-floor cars are operated as the ‘trench’ passageway between the wheels can be wider; for example using Indian Gauge (1676mm/5ft 6in) could give an aisle width some 230mm wider than a standard gauge low-floor car. Unfortunately the space outboard of the wheels and within the Dynamic Kinematic Envelope of the car will be reduced – which may cause a space problem if outside longitudinal or wheel motors are to be employed.
In the early days of San Francisco’s BART, a study of car dynamics claimed that a wider gauge gave a better quality ride for the passengers. I am not sure exactly how this exercise was done. It would be of interest to know if experience over the years has justified the decision and how the determination might be made.
It was also claimed that a wider gauge was required for safety if the cars were to cope with high winds on the Golden Gate Bridge. However, many believe that BART covered its engineering decisions by implying the safety aspect which no-one would question (standard gauge Key Systems cars used the Bay Bridge for nearly three decades with no problems). I suspect that the real reasons are that the non-railway engineers involved in the project wanted to be seen to be offering ‘something different’ to that which had gone before and wished to keep the production design of the system in-house.
Presumably BART and others who have followed have found, like the Russians, that it costs little more to have a special track gauge for a closed system when the operator orders cars hundreds at a time. It is only the single car that has a significant price difference for the non-standard. The 2010 base price for both the Prague and Riga ForCity appears to be EUR3.7m in spite of Riga using a track gauge wider than the Western standard and that all other Škoda low-floor trams are standard gauge. The only differences between the Prague and Riga versions are the bogies, and the the Prague version has all wheels powered and the Riga version has four unpowered ones. It is unlikely that there is anything special or costly about metre or Russian gauge (1524mm/5ft) rolling stock.
It would seem that the engineers are being forced to operate in the tight triangle of space where the trajectories of politics, finance and physics overlap, but do not necessarily meet. A change in one will drive the outcome.
Historically, the decision to prescribe a gauge of one metre for all Swiss tramlines has been seen as part of a political decision that would prevent standard gauge heavy rail goods wagons being run through the public street. This may have had some validity in the early days of railway construction, but the later growth of the metre gauge secondary lines in Switzerland eroded the differentiation between tramways and railways.
Conversely, the choice of the odd 4ft 73/4in (1416mm) gauge for the first-generation tramway in Glasgow, UK, was precisely because this permitted standard gauge goods wagons to traverse the streets to reach riverside shipyards. Some of the reasons put forward to justify BART’s odd gauge have been discussed above, but it is also thought that the gauge was chosen to prevent other railroads getting running rights over the BART Transbay tunnels into San Francisco.
The choice of a wider gauge in Stuttgart and the Bay Area may also have been made to show that the new transport system was ‘newer and therefore better’ than what had gone before – a typically crass political view.
If politics can produce strange decisions then financiers, often with little knowledge of engineering and even less of transport systems, can make equally odd choices. They will tend to think that what is the most common must result in economies of scale, thus reducing capital cost and maximising the return on investment. This view will not be tested and the financiers will be encouraged by the car builders and track manufacturers who will want to lock buyers into buying their off-the-shelf products.
One of the many peculiarities of the various PFI/PPP financial models used for modern urban rail systems is that the financiers will want to show that the rolling stock has some residual value and could (in theory) be moved from a financially ailing system to another, thus protecting the investment and revenue stream. The fact that this has almost never happened does not influence the view.
It is also claimed that buying ‘standard’ items of stock can drive down price by joint ordering with other systems. Again this usually proves almost impossible to achieve in the real world. Most governments only seem to be able to fund one new system at a time and this makes joint ordering difficult, although we have seen occasional examples of one system using the ‘options’ of another to bring down vehicle prices and decrease lead times.
The physics of tramway systems seems to show that for the broad range of performance parameters set for modern systems – cars up to 2.65m wide, running to a maximum operating speed of 80km/h (50mph) – any gauge between about 3ft and 5ft 6in will do.