This diagram shows how BR's obtruding platforms would present a problem in adopting the standard Continental width (line running through platform edge). Increasing the structure gauge to give extra height, for the GB+ loading gauge needed for unaccompanied piggyback or the GC gauge required for tractor-and-trailer piggyback, would be very expensive. The black box shows the SB1 loading gauge RfD has adopted for Channel Tunnel containers and swap-bodies. 'Universal' gauge is the West European standard for vehicles.
From Modern Railways, April 1992
Berne and all that
With the opening date of the Channel Tunnel galloping towards us, the new route for what was to be called the New Kent main line fixed by the Government though not funded, and suggestions afoot to provide new freight routes to the Midlands and the North across the East Anglian flatlands or using bits of the former Great Central, it seems appropriate to provide readers with a little more background information on the loading gauge question.
The short answer to the question 'What is the Berne gauge exactly?' is that it doesn't exist. That would not be very helpful, however. The term Berne gauge is a useful shorthand expression, used only in Great Britain, for one of the four internationally-agreed loading gauges used on the European mainland. There are two other widely-used loading gauges in Europe which are not internationally agreed, namely the British and the Scandinavian. The British, as all readers will know, is both lower and effectively in certain respects only, narrower than any of the four internationally-agreed gauges: the Scandinavian is the same height as the highest of the international gauges but considerably wider, so that ordinary Swedish and Norwegian coaches cannot run generally in the rest of Europe.
The term 'Berne gauge' arose first from the fact that a conference was held in that city in 1913, which tried to improve on the gauge then generally accepted for vehicles in international traffic, without the need for each individual design of vehicle to be submitted to every railway over whose lines it was proposed to run it.
The original (1891) gauge meant everyone accepting the then standard French loading gauge, which was the smallest in mainland Europe as to both width and height. All the other railways had very similar width requirements, and the new gauge defined was only some 50mm wider. However, the new gauge raised the height by some 130mm, as an attempt to compromise between the French standard and the generally more liberal heights available elsewhere. But it took quite a long time before all French main lines conformed to it, particularly in the west of the country, and full clearance was not achieved until the late 1930s.
The gauge thus defined (shown on the diagram in the main article on the preceding pages as Universal gauge) continued to be known officially as the Gabarit passe-partout international, or 'PPI', which translates literally as 'pass everywhere international gauge'. The convention which brought it into use was signed in Berne at the end of the conference mentioned above, hence the unofficial name Berne Convention gauge, shortened to Berne gauge. It came into force on 1 January 1914.
At the same time, the height permissible in Belgium, and throughout Central Europe (to all intents and purposes, the countries comprising the German and the Austro-Hungarian Empires), plus a small number of other lines, was, almost from the beginning of railway con- struction in those countries, considerably greater. Most of these railway were in the Verein Mitteleuropaischer Eisenbahnverwaltungen or 'Union of Central European Railway Administrations', which retained for intemational traffic within its own region this greater height allowance.
Latterly, long after the formation of the UIC (International Union of Railways), of which the four main-line railways of Great Britain were members, UIC A gauge was formulated, marginally higher than the PPI gauge. A slightly higher gauge, but still lower than that available in Belgium and Switzerland became UIC B gauge, while the 'Central European' gauge became UIC C gauge. This is an over- simplification of the process, but is accurate enough to describe approximately the situation existing a few years ago. All these gauges had identical widths, which stretched from the Spanish to the Soviet or Russian frontier, except for Scandinavia.
The need for very high clearances was never apparent for ordinary passenger or covered goods wagons, but was useful for the carriage of timber, hay and straw and awkward indivisible loads. In recent years however, it has become more important, because of the spreading use of containers and swap-bodies, and the desire to piggy-back complete commercial vehicles. All these are comparatively narrow, 2.5m or 8ft 2.5in for swap-bodies or commercial vehicles, and 8ft or 8ft 6in (2.437m or 2.6m) for containers. However, they are mostly flat-topped, and therefore carry their full width right up to their height. Thus even an 8ft by 8ft container will not go on a standard floor- height flat wagon in the UK, while the newer 8ft 6in, 9ft and 9ft 6in high containers require even lower floor-heights. The 9ft container can even give problems on standard height wagons on lines to UIC A gauge. The problem is never in the centre of the gauge, but always at the sides.
While BR has therefore been concentrating on easing the W6-gauge clearances for containers of the larger heights on Freightliner wagons (or equivalents), by cutting-back bridge shoulders without raising the crown, similar work has been going on in France and Italy to accommodate the higher loads without having to have recourse to very small-wheeled wagons. SNCF (which has already cleared many main lines to B gauge) is clearing all main lines to the relevant gauge B+. BR is also looking at a higher gauge than the modified W6 (known as W6+ or W6A) without increasing the general gauge width, which is unnecessary for swap- body or container traffic. The new gauge is known as SB1, but is still 470mm lower than UIC B+.
The Swiss, who are determined to keep the 2.5m, 40-tonne lorry off their roads, are busy clearing the main trans-alpine transit route to Gauge-C clearances, so as to be able to accept almost all normal lorries as piggyback traffic over the St Gotthard route from Germany to Italy.
Nothing has been said about the width differences between the four UIC gauges (A, B, B+ and C), all of which are the same, and the BR gauge. The reason for this is that it is relatively unimportant for inter-modal (container/swap-body) freight traffic, which will form the vast majority of the Channel Tunnel rail-freight traffic, nor is it important for heavy bulk traffic in tank or bulk grain wagons which can already carry greater loads within the BR loading gauge than they can carry on the mainland, because of the higher permissible axle-load on BR than on any other European main-line railway (25.5 tonnes on BR and 20 or 22.5 tonnes elsewhere).
For passenger traffic, the width difference is also relatively unimportant (although for sleep- ing cars only, the height difference is not; one cannot get three berths one above the other within the BR loading gauge). This is because the way that the UIC gauges are defined creates a far greater reduction in permissible width with increasing length, than is initially the case with the BR gauge. Thus while the short-wheel- base four-wheeled goods wagon of yesteryear would be a full foot wider on the mainland than here, the standard 26m-long UIC passenger coach has to be no more than 2,825mm wide. For the imperially minded that is 9ft 3.Sin, which is (surprise) exactly the overall width over door handles on a BR Mk 1 coach.
When BR produces its 26m coaches for IC250, they are unlikely to be much narrower than the Mk 4, which will be unnoticed by the passenger compared with the UIC coach. It is only at the bogies, where there is no throwover, and generally below platform level, where the BR gauge is even narrower, that coaches built to UIC gauge can be noticeably wider, which is why the Trans-Manche Supertrains have had to have their bogies radically redesigned from those used on the TGV-A trains, although the car-bodies are literally but a few millimetres smaller, at 2,814mm according to the published drawings.
And just for the historical record, it is worth recalling that the late-1930s Cornish Riviera Limited' stock was 9ft 7.5in or 2,938mm wide, more than 100mm wider than today's standard 26m-long UIC coach, albeit only about 19m long. It is also worth recalling that the sleeping cars for the 'Blue Train' and the Pullmans for the Fleche d'Or were all built in Birmingham and travelled to Harwich for the train ferry, with some passing clearance difficulties - but they got there.
TheTonbridge-Redhlll line is being electrified, with clearances increased for Channel Tunnel freight services. Third rails are in position on 16 November 1991 as the 14.43 Tonbridge-Reigate (No L836) negotiates the recently-lowered slab track in Penshurst tunnel. C.B. Scott-Morton
From Modern Railways, April 1992