Brunel and the Broad Gauge

A recent post on a Facebook group regarding I K Brunel’s selection of the broad gauge for his Great Western Railway reminded me of some recent correspondence I had on the subject.

Ultimately, the question of ‘standard' gauge, 4’ 8½” or ‘broad' gauge, 7’ ¼”, was decided, like the now defunct duel between Betamax and VHS videotape recorders, by the marketplace. And in both cases, the technologically inferior solution—4’ 8½" and VHS—won out.

L T C Rolt’s definitive biography of Brunel, published in 1957, provides some very interesting insights into why the so-called standard gauge was chosen in the first place. On page 107 et seq., he points out that 4’ 8½” was the width of the ‘early coal-wagon ways of Tyneside’. They were mostly pulled by horses, and it was a suitable space between the rails in which a horse could comfortably walk. Rolt continues: ‘It was natural that George Stephenson should have accepted this precedent ... on the Stockton and Darlington railway (1825)...’ part of which initially used horses to pull the wagons. George Stephenson then went on to become engineer on the Liverpool and Manchester railway (1830), the first proper commercial railway. Rolt goes on:

[that was] the moment for him to have considered whether so narrow a gauge was ... the most desirable for trunk lines of a public railway ... when Robert Stephenson was asked by the Gauge Commissioners whether his father had actually advocated the gauge of 4’ 8½” for the Liverpool and Manchester he replied: “No. It was not proposed by my father. It was the original gauge of the [private] railways around Newcastle-on-Tyne, and therefore he adopted that gauge.” This classic non sequitur betrays the conservative rule-of-thumb method which the conscientious and careful but unimaginative craftsman so often adopts when he ventures into strange fields.

And that is the nub of the issue. The 4’ 8½” gauge—as applied to the great commercial railways—came about almost by accident.

It has always been assumed that Brunel selected his broad gauge primarily from considerations of stability at high speed, however it is instructive to see what the man himself had to say on the subject. On 15 September 1835, IKB wrote a long letter to the directors of the GWR on the question of gauge.* He said that friction in the axles of the locomotive and carriages was a primary source of resistance—leading to lower speeds or more power being needed—and that the effect of this was reduced as the ratio of the wheel to the axle diameter was increased.

Using the Stephensons’ 4’ 8½” gauge with large wheels meant that the locomotive and carriages would need to be excessively high—since the wheels and springs would need to be accommodated below them—and therefore inherently unstable. Using a wide gauge, where the wheels were beside rather than underneath the locomotive and rolling stock would, as well as reducing friction losses, lead to steadier motion and less wear and tear on rails and carriages. 
 
Brunel goes on to refute the various objections to a wider gauge—wider embankments, tunnels etc., extra weight, friction on curves, but concedes that incompatibility with the London and Birmingham railway—with which the GWR had originally planned to share a London terminus—was a serious obstacle. In the event, the plan to share a terminus was dropped, apparently for other reasons, so even that objection was considerably reduced.
 
Believers in the conspiracy theory of history might wonder whether Isambard was using smoke and mirrors here. Did he aim to bamboozle the board into accepting a critical aspect of design that would be more expensive to build—and ultimately very costly when eventually the line had to be converted to standard gauge—but one that he was convinced was better? Nevertheless, it is an unavoidable fact that however good the lubrication of the wheels was, an average train would have had dozens of axles in the locomotive and carriages, all contributing friction.
 
It is also true that the broad gauge allowed the main driving wheels on the early locomotives to be enormous, and this would have given them greater ‘grip’ on the rails during wet or icy weather, although IKB does not mention this in the letter.

At the time that the GWR had committed to broad gauge (c 1835) there were very few other railways extant. Brunel insisted on engineering best practice—as he saw it—and this always trumped questions of cost or long-term benefit, to the despair of his directors.

As new railways came along, built by others than the Stephensons and using engineers with less insight than I K Brunel, it was natural that they should ‘follow fashion’, although this was not without rationale. When Brunel was building the GWR, Robert Stephenson was constructing the London and Birmingham Railway which commenced in 1833. With the L&BR running north into the heart of industrial England, it was inevitable that the many railways adjoining it would need to be compatible with it. The fact is that the ‘industry’ in the West Country, served by the GWR, was mainly agricultural, and there was not the same drive there to criss-cross the land with railways.

One suspects that even had Brunel known what was going to happen, vis a vis the dual gauge and the final and expensive change back to George Stephenson’s coal-wagon gauge in the 1890s, it is unlikely that he would have changed his mind. He would have insisted that 7’ ¼” was the only viable gauge—the quality of the ride and the speeds obtained proved it—and the GWR and Brunel were the ‘only ones in step’. In fact, when it came to decision time there was so much installed track built to the Stephensons’ gauge, that changing just the GWR was an inevitable no-brainer.

As a further addendum, Rolt notes that the original colliery gauge was 4’ 8”, and that at the design stage of the Liverpool and Manchester railway 'An extra half inch was added by some person unknown to fame…' Likewise probably, the extra ¼” added to the broad gauge of seven feet…

* The letter is reproduced on page 17 of volume 1 of the History of the Great Western Railway, by E T MacDermot.