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Track Gauge & Loading Gauge

The distance between the inner faces of the rails is called the gauge. The first railway to use what became the 'standard gauge' of four foot eight inches (1.4m) was the Willington Colliery wagonway, built by George Stephenson in 1765, it used wooden rails and flanged wheels. Subsequent railways built by Stephenson, such as the Stockton and Darlington and the Liverpool & Manchester, also used the four foot eight inches gauge. This changed to four foot eight and a half inches as points or turn-outs were developed to allow tracks to divide and join. This was by no means universal however and in the 1830's there were lines laid with five or six different gauges across the country and even today Glasgow's underground railway system uses a four foot gauge track.

Early Railways in other countries were in the main built by British engineers or used British design philosophy and although 'metric' most adopted the four foot eight and a half inch gauge. Not all countries settled on the 'standard', Spain and Russia got their engineers from Scotland and settled on five foot six inches (1.68m) while Ireland opted for five foot three inches (1.6m). The widest track I have found reference to in the UK was at an iron works at Motherwell with a gauge of ten foot eleven inches (3.33m).

Brunel, chief engineer of the Great Western Railway in the late 1830's, developed a seven foot (2.13m) gauge, usually called 'broad gauge', which was the only serious competition for Stephenson's standard gauge. The track was laid as 'baulk road', as described in the section on Track - Development History this consists of long heavy timbers laid under the rails with cross-timbers at intervals to hold them apart and the wide track with fewer cross ties gave these lines a very distinctive appearance. The GWR was a successful enterprise and this seven foot gauge was adopted by several companies in the South West of the country, the problems came where goods had to be shifted from wagons on one gauge to wagons on another, a practice called 'transshipment'. In the early years all went smoothly enough but as traffic levels soared there were major delays at the transshipment points and with the rapid expansion of railways in the 1840's the question of gauges became a matter of major debate.

The government set up a commission to look at the question and in 1847 the 'Gauge Act' was passed favouring Stephenson's gauge and referring to this as 'standard gauge'. The seven foot 'broad gauge' developed by Brunel was effectively prevented from spreading by this act. At the time there were about two thousand miles of 'standard gauge' in place as against about two hundred miles of broad.

Quite a lot of Brunel's broad gauge track was altered to 'dual gauge' by adding a third rail but in the 1890's the last of the broad gauge lines were converted to the standard gauge in a single large scale operation. Do note however that much of the 'baulk' type track was simply modified, sections of 'baulk road' modified to standard gauge remained in use into the 1930's and a few sections were still seen in the 1940's. This modified track had a distinctive appearance due to the comparatively wide spacing of the cross-ties but it can be modelled using standard Peco track if required.

Fig___ Baulk road modified to standard gauge

Sketch showing how standard model railway track can be modified to represent re-gauged baulk road track

Today the gauge is set at four foot eight and three eighths inches (1.432m) and is maintained to an accuracy of better than a tenth of an inch (2.5mm) to allow high speed running.

Clearance between tracks

The Liverpool & Manchester Railway of 1830 was the first line to use double track all the way, they used left handed running on their double lines from the start (only a few companies in Britain used right handed running and these had all changed to left by mid nineteenth century). Stephenson designed the track for the L&M with a gap between the inner rails of the two tracks of four foot eight and a half inches, the idea being that unusually wide loads could be carried on trucks running on the inner rails of both tracks during slack periods. This left very little clearance between the lines and on the opening day of the L&M an MP called Huskisson, who had championed the railways, stepped down to stretch his legs at a watering station and was caught between a coach and a passing loco. This took off his leg and he died from his injuries, becoming the first recorded main line railway fatality.

The distance between the inner rails on double track lines was subsequently standardised (more or less) at six foot (1.82m), widening on curves. Different companies adopted different spacings but BR standardised the spacing, Mr J. T. Raven (a retired Railway Civil Enginner)was able to advise:
The dimension of the British sixfoot was arrived at by using the size of six feet (Outside edge of rail to outside edge of rail) plus twice the width of the railhead (2.75 inches) giving a sixfoot of 6 feet 5 1/2 inches or 1968.5mm, this may have been rounded up to 2000 mm.
The gap between the running lines is sometimes referred to as 'the six foot way' and railway staff often refer to the area between the rails as 'the four foot'.

The distance between the running line and a siding was greater, BR settled on a minimum of ten feet as there was the likelihood of someone walking along the siding, for example a wheel tapper checking the wheels on the stock. Where additional running lines were added under BR the distance between these and the main running line was to be ten feet, although this could be reduced to nine foot where space was restricted, existing multiple track lines were not affected by this however.

This spacing set the upper limit on the width of items that could be carried on the line as allowance has to be made for trains carrying loads heading in opposite directions. This allowance was further narrowed to allow for what happens on curves when the centre of the outer vehicle, which is 'cutting the curve' passes the ends of the inner vehicle which are riding directly above the inner track or possibly even extending slightly beyond (although as noted above there was some widening of the space between tracks on the curves to increase clearances).

Loading Gauge

The 'Loading Gauge' is the maximum size for rolling stock to allow clearance under bridges and between tracks, especially on corners. It was established quite early on that the maximum width allowable for high speed running was in the region of 2.5 times the distance between the rails, on narrow gauge lines this is often exceeded but speeds tend to be slower. The British loading gauge reflects the basic motivation of the original railway builders, namely to shift coal and ores in bulk from place to place. In the UK the standard clearance was therefore defined with relatively small wagons in mind. To refer to 'the' loading gauge is however misleading as it is only since the advent of British Railways that a national standard has been defined, and this cannot easily be applied to older lines built with smaller clearances.

The sketch below, scanned from a 1930's carriage and wagon builders pocket book, shows the average for England and Scotland and may be taken as a fair approximation for most mainland British standard gauge lines (a more detailed drawing, from the same source, showing the suggested details for British suburban passenger stock has been included in Appendix Three, under Loco Hauled Passenger Coaches).

Fig___ Average British loading gauges
Sketch showing Average British loading gauges

The loading gauge adopted as 'standard' by British Railways was based on the more common clearances on the pre nationalisation railways but at the generous end of the scale. As work was done on the line the clearances were increased, where possible, to conform to the national standard. This allowed a maximum width of about nine feet six inches up to a height of about ten feet and a maximum height of about thirteen feet six inches from the top of the rails in the centre. The Loading Gauge also specified the location of couplings and buffers, buffers were set five feet nine inches apart and set three feet six inches above the top of the rail.

Until the advent of the ISO rectangular container the biggest things on the railways were passenger carriages, on the GWR broad gauge lines some main line coaches were built that were about ten feet wide, at the opposite end of the scale were lines such as the SECR where coaches were typically only eight feet wide (the SECR also had their tracks closer together than most companies and as a result retained the rooftop 'birdcage' lookout for the guard long after other companies partly because there was no room at the sides for a look-out ducket). Even within a single company the actual loading gauge could vary a lot, the largest passenger coaches on standard gauge lines were those built for the Lancashire & Yorkshire Railway's electrified service between Liverpool and Southport which were a fraction over nine feet ten inches wide, but these were built for and confined to that route. When the GWR changed from broad gauge to standard gauge their generous clearances often allowed a second track to be run into goods sheds and a third line to be run through double tracked stations on former broad gauge lines. When they switched to standard gauge however they adopted a smaller loading gauge similar to other main line railways and built most of their stock to this smaller gauge to allow through running. The former GWR broad gauge lines have the most generous clearances on BR with thirteen foot six inches (4.1m) vertical clearance and nine foot eight inches (2.9m) width at the widest point but this is tight by European and American standards. In Europe they settled on a standard of fourteen foot (4.2m) high by ten foot (2.3m) wide and in the USA, where the main impetus for railways came from the need to shift beef `on the hoof' from the Midwest, the loading gauge is about fifteen foot (4.6m) by ten foot (2.3m).

Most British goods stock was roughly eight feet wide, possibly the widest single vehicle being the guards van with side look-outs and the BR standard van was only eight feet nine inches wide at the duckets. The widest early BR era goods vehicle I know of was the 'ferry high open' (as per the Peco long wheelbase tarpaulin wagon) which was eight feet eight inches wide over the side posts.

The air braked stock introduced after 1971 was rather larger, the standard four wheeled open wagons and vans were about eight feet ten inches maximum width to make them a better match to the standard pallet sizes. Curtain sided air braked vans for palletised traffic then ran into problems when the load was not properly secured, if it toppled sideways it could cause the side to bulge 'out of gauge'.

Some loads were light but bulky, bags of charcoal, nested stacks of empty fruit baskets and loose hay to feed the horses being examples, such loads could be piled very high on an open wagon. Spotting a load overhanging the sides was comparatively straightforward but judging its height was more difficult. To allow staff to check that loaded wagons would fit under bridges and through tunnels a simple suspended frame, also called a loading gauge, was introduced. This consisted of a post with a curved rail suspended from it, shaped to the clearances on the line. Virtually every railway goods yard had one of these and loaded wagons were passed underneath before dispatch to make sure they remained within the gauge.

Fig___ Typical loading gauge used in goods yards
Sketch of a typical loading gauge used in goods yards

Although broadly similar these devices were not all the same, aside from the differences in construction and complexity different lines were built with different clearances and individual companies had differing policies. Where a station was jointly served by two companies, say the LMS and the GWR, it was common practice to have a loading gauge with hinged sections at the ends of the suspended bar which could be set for the differing requirements of the two companies.

The loading gauge, in the sense of the clearance provided around the track, also affects the length of railway vehicles. Long coaches and wagons, or long loads carried on several vehicles, cut the corner on curves, also the ends of long loads tends to stick out on curves and where two meet in transit a collision becomes likely. Long loads could be accommodated but only if they did not extend to the full width of the gauge, and even then due to the nature of the tilt or 'super elevation' of the track (which is 'banked' up slightly round curves) long and high loads had to be carefully routed.

As a general guide anything shorter than forty foot (12.2m) could be up to the full width of the gauge, anything between forty and fifty foot (15.2m) long could be up to about nine foot (2.7m) wide whilst loads between fifty and sixty foot (18.2m) long had to be less than five foot (1.5m) wide. Anything longer than sixty foot usually had to travel as a special train with a time table that meant it never encountered another train on a curve. In practice these widths were very much an upper limit and only applied on main lines, where branch lines or lines in industrial areas were concerned the upper limit on the width of a load was typically about eight feet. In the early twentieth century passenger coaches were built with lengths of up to seventy foot (21m) and extending to the full width of the loading gauge but these were very restricted in use. Since the Second World War a number of lines have been widened to allow longer vehicles and the current standard coach lengths are between 20m (65' 7") and 23m (75' 7") with the latter size still having some restrictions on its use. There was a line on the South Coast, I think it was the branch to Hastings, where as an economy measure the clearances were made very tight indeed. One tunnel in particular was exceptionally tight and the passenger coaches for this line had to be specially built to fit within these tight clearances. I seem to remember there were problems with diesel locomotives, some being modified specifically for use on this line. Clearances on the Burry Port &Gwendraeth Valley Railway in South Wales were so tight that four wheeled passenger coaches remained in use up to the end of passenger services in 1953 and in the subsequent freight-only years class 03 and 08 engines had to be modified with a low roof to fit under the bridges (the line remained in operation for coal traffic until 1996).

Containers are a good example of how the loading gauge can affect traffic. The original specification for the modern rectangular metal container came from the US defence department and specified a box eight feet high by eight feet wide. As the floor of a standard wagon is about four feet up the upper corners of the container were wider than the curved top of the loading gauge allowed. They could only be transported on British lines using drop-centre wagons or the purpose built 'Freightliner' low floored wagons. Later containers eight feet six inches high appeared, for which the clearances on British lines became a problem. Following a great deal of work by Railtrack and some innovative designs from the wagon builders the eight foot six inch high ISO container could be handled on most of the railway network by the mid 1990's. Even larger containers then appeared and a new variant the 'swap body' (a container designed to function as the body of a lorry trailer and built slightly wider than eight feet to better accommodate the standard European pallet) appeared and dealing with these higher containers and wide swap-body traffic will involve a lot more work to increase bridge and tunnel clearances. The revised loading gauge clearances required to carry nine foot six inch high containers and lorry trailers to the current maximum road size (fitted with special suspension to lower its overall height when on the railway wagon) were generally referred to as the PB Gauge standing for Piggyback Gauge. The clearances for allowing nine foot six inch high containers to run on standard flat wagons were rather smaller and the loading gauge clearances to permit this were known as GB+ Gauge. There were plans are to modify two lines from the channel tunnel to London where there would be a short link line connecting the East and West Coast Main Lines, each of which would be modified for swap-body vehicle clearances. This is in line with a European plan for a high-speed railway freight system extending right across the Continent then via the Channel Tunnel to the industrial centres of Britain. The organisation sponsoring the modifications to British tracks is called the Piggyback Consortium (one of the vehicle types they are interested in promoting is a wagon to carry road trailers and this is usually referred to as a 'piggy-back train' following American practice). At the time of writing all this work is under review and may not be implemented.

Updated information
The Piggyback Consortium was working with Railtrack on the project to improve clearances from the Channel Tunnel and thence up the west coast main line (WCML) to Glasgow. The plan to similarly enhance the East Coast Main Line (ECML) to PB Gauge was shelved quite early on but as the WCML provided access to the majority of proposed customers this was accepted by the Consortium. By this time Thrall Eurospine trailer carrying wagons were in service with EWS for Parcelforce trailers between London and Glasgow, Freightliner had bought some trailer carrying wagons from a company called Charterail which carried specially built (smaller than normal in width and height) lorry semi-trailers) and Babcock's first MEGA 3 pocket wagon was being trialed by Freightliner. Both the Eurospine and the Mega 3 designs allow standard width but low height trailers to be carried, they were suitable for tanker trailers and trailers carrying heavy loads (these being the only ones able to fit inside the loading gauge). These wagons can also carry deep-sea containers and swap bodies.

Railtrack then (in 1998) decided not to bother with the upgrading at all. The reasons for this change in policy were never made clear however the Consortium noted that there was actually no freight capacity at all south of Milton Keyenes during the day. The limitations of network capacity following the various cutbacks in rail routes since the 1960's meant that freight operating companies (never as politically sensitive as passenger services) would always struggle to find routes for their trains.
Railtrack then suggested that a limited project to allow the carriage of nine foot six inch high containers would 'satisfy the market'. The consortium pointed out that:
Lorry semi-trailers carry 74 per cent UK's road freight (measured in tonnes-km in 1997), and the majority of these (about 75 per cent) are built to the largest permissible size to enable them to carry the greatest volume. They also carry 75 per cent of general cargo between the UK and the continent. This preponderance of high-sided lorry semi-trailers is evident on all major motorways.
It is this large market for the highest semi-trailers that piggyback seeks to attract to rail. With the exception of the niche but still significant tank and heavy goods market, which can be carried by rail at present, the customers (logistics service providers and many RHA/FTA members) demand the greatest trailer height to achieve volume. They are not interested in purchasing specialised equipment which carries less volume just to enable it to be carried by rail.
The effective maximum height for trailers engaged on international journeys is 4 m road mode. On rail, with the air springs deflated, this height of trailer plus the rail wagon just fits into PB gauge. It also happens to fit just within the GB+ loading gauge, which is the standard in all parts of Northern Europe and on selected routes between the Channel Tunnel and Italy.
Deep-sea containers (boxes) are carried between ports such as Felixstowe, Southampton, Tilbury, and Liverpool to centres of manufacture or consumption. Their height varies, generally between 8 ft 6 in and 9 ft 6 in.
Whereas the 8 ft 6 in boxes are carried today on the main routes in Britain on standard rail flat wagons, the newer 9 ft 6 in high boxes cannot be carried on such wagons within the existing loading gauge.
The 9 ft 6 in boxes now comprise 10 to 15 per cent of the market with this share growing rapidly. If the railways wish keep their market share, let alone increase it, they will have to raise the gauge height to accommodate the 9 ft 6 in high boxes on flat wagons or build special low wagons at extra cost. This new gauge (called here the "9 ft 6 in gauge") is 230 mm (9 in) lower than PB gauge.
The main market for piggyback is alongside congested motorways, particularly the M1 and the M6. That is why Railtrack, at the time when it was supporting piggyback, chose the West Coast Main Line for the piggyback upgrade.
The 9 ft 6 in container traffic however needs to access to major deep-sea container ports: Felixstowe, Southampton, Tilbury and Liverpool. This particularly affects the Nuneaton-Peterborough-Felixstowe and Birmingham-Reading-Southampton routes.
Both the PB gauge route from Glasgow to the Channel Tunnel and the 9 ft 6 in gauge for deep-sea containers to ports are described in Railtrack's 1998 Network Management Statement.
We understand that Railtrack has argued that a network of 9 ft 6 in gauge routes as described above will be able to capture 90 per cent of the "market". We question which market. If it is the deep-sea container market, that may be correct in the long term, and the proposed upgrade to 9 ft 6 in gauge on these routes is very much to be welcome.
However, such a gauge can probably only cater for less than 20 per cent of the lorry semi-trailer market which, although welcome, is still only a niche in a very much larger market, and on routes which generally follows congested motorways such as the M1 and M6. These routes require PB gauge to make any significant inroad into the lorry semi-trailer market.
Thus, there are two very different markets, with some small overlap. They should each be treated on their own merits, not mixed and confused.

They went on to question the maths used by Railtrack to establish the cost of the proposed upgrading. To the untrained eye, such as mine, the basic problem seems to have been that Railtrack were unwilling to undertake such a massive investment as this was slightly risky and might not provide the benefit to their shareholders that a less ambitious, passenger oriented, plan would achieve.

Loads which are wider than the gauge are no longer carried by rail but prior to the development of roads and road vehicles, and the withdrawal of the common carriers legislation, the railways often had to deal with such 'out of gauge loads'. When these loads were moved through the system they had to travel as special trains and the railway companies planned the routes for these loads with great care, detailing points where they might foul adjacent sidings (which had to be cleared) or where they might safely be passed by another train. When moving exceptional loads such as bridge girders, it was sometimes necessary to take the train onto the 'wrong line' in order to put it on the outside track on a curve through a cutting or under a bridge.

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