Why 4’8 1/2”?

[Bevan Price]

As I understand it, Brunel chose broad gauge primarily as he considered it safer due to the lower centre of gravity of the wider railway vehicles which resulted in them being more stable at higher speeds.

But it is more expensive to construct as you need to buy more land (and longer sleepers).

 

[norbitonflyer]

Aha. This allows me to wheel out, again, my favourite railway fact:

To three decimal places….

Standard gauge is Pi/2 yards

Not only that, but 4' 8.5" is 56.5 inches: near enough to the number of degrees in a radian (57.3) Which means that on standard gauge, superelevation in inches is equal to the cant angle in degrees.

 

[12LDA28C]

But it is more expensive to construct as you need to buy more land (and longer sleepers).

Indeed. Clearly he considered that a price worth paying.

 

[Chester1]

And this raises the question, if instead Ireland had standardised on 4ft 81/2in would the railways there be in better shape today, as they could buy 'off the peg' rolling stock

They are in a similar situation to GB because of our wider loading gauge. Having the same track gauge as the continent isn't very useful on its own. It's telling that the modern GB and Dublin trams were designed where possible to European track and loading gauges.

 

[HurdyGurdy]

Not only that, but 4' 8.5" is 56.5 inches: near enough to the number of degrees in a radian (57.3) Which means that on standard gauge, superelevation in inches is equal to the cant angle in degrees.

The cant angle is measured over a base which is the distance between rail centres. You have add on the width of a rail head to the distance between gauge faces. Rails which were designed in inches typically had vertical gauge faces and that base would be 56.5 + 2.75 inches.

 

[Merle Haggard]

But it is more expensive to construct as you need to buy more land (and longer sleepers).

Maybe that was why Brunel used the 'Baulk Road' - longitudinal beams under each rail.

Interesting thought, how much narrower would the gauge have to get before speeds were limited due to the gauge. 4ft 81/2 inch has been tested upto over 350mph by SNCF, and the track was new but standard, although there were a lot of other tweaks to get to this speed, higher catenary voltage and larger wheels are two that come to mind. There are regular 200mph or a bit more services in various countries. So assuming you wanted to acheive 200mph but didnt want to go any faster and wanted to use standard flanged wheel on rail.

Would the 4ft 8in railways during the 1840s have been able to support the speeds that the GWR was acheiving on 7ft? The designs and engineering was much simpler?

I find the whole area of how railways developed interesting.


I think that was the principle of the Surrey Iron Railway

The L.N.W.R. constructed two locos to demonstrate that high speed was possible on standard gauge; Cornwall and a Crampton type 6-2-0 loco - possibly as evidence to the Gauge Commission. Both had very large driving wheels; original drawings suggest that the driving axle of Cornwall passed over the boiler, and the Crampton had similarly large driving wheels using the Crampton principle, the driving axle was in the space behind the firebox. Cornwall, much rebuilt, is still around; there are stories of it achieving speed into 3 figures in its heyday. Perhaps the choice of name was intended as a challenge to Brunel, who was still working his way westwards through Devon at the time.


//I would suggest that bogie hunting is greater if the ratio of wheel base to gauge is lower; to achieve the same stability as an 8' wheelbase standard gauge Bodie, a broad gauge one would need to be about 12' w.b., even longer when 9' and 9' 6" became standard on the narrower gauge.

 

[ThirteenArches]

Crampton... can't resist posting this: Something wicked this way comes.... and just for fun, 4'10" gauge too.

 

[Oxfordblues]

A bloke in a pub many years ago told me that when the Irish decided to build railways they sent an engineer over with a tape-measure to report back on the British track gauge. Misunderstanding his brief, he measured the distance between the outside of the rails and thus 5'3" was adopted. Whether true or not, this meant that train-ferries would not be an option for Anglo-Irish traffic and thus a system of lift-on-lift-off containers was developed. This in turn led eventually to the worldwide containerisation of most non-bulk traffic and the system we see today.

 

[Gag Halfrunt]

Among other mistakes they went for a gauge of 5'6", only otherwise seen in India and neighbouring countries.

As well as Argentina and Chile.

I bloke in a pub many years ago told me that when the Irish decided to build railways they sent an engineer over with a tape-measure to report back on the British track gauge. Misunderstanding his brief, he measured the distance between the outside of the rails and thus 5'3" was adopted.

That's an urban myth.

One question that is frequently asked is why Ireland has a gauge (distance between the rails) of 5ft 3in (1600 mm) instead of the most common ‘standard’ gauge, 4ft 8½ inches, especially as all of Ireland was part of the United Kingdom at that time. Indeed, the Dublin & Kingstown Railway was initially built to George Stephenson’s gauge of 4ft 8½ inches, but circumstances would soon change, leading to Ireland’s distinctive gauge.


The problem arose when the Ulster Railway began to construct its line between Belfast and Armagh. They chose the gauge of 6ft 2in, and the proposers behind the planned Dublin and Drogheda Railway were going to build their line to a gauge of 5’2″. Immediately this caused political wranglings, as the different gauges between Ireland’s three railway would lead to the problems faced by railways across the water in Great Britain – where trains from one railway could not run on another.


At this point, the Board of Trade stepped in and asked Major-General Pasley of the Royal Engineers to examine the situation. After ruling out Brunel’s 7ft broad-gauge he asked the opinion of the Stephensons their opinion, who (while committed to 4ft 8½ in GB) suggested a compromise gauge for Ireland between 5ft 0in and 5ft 6in.


It was at this point that Major-General Pasley discovered that the exact average between all three gauges was 5ft 3in, and so made his recommendation that this should be the standard gauge throughout Ireland, which was readily accepted by the Board of Trade. A brilliant example of a political compromise! Naturally, the Dublin and Drogheda enthusiastically accepted the ruling (only being one inch out), while the other two parties were probably not so pleased…


The gauge of the Ulster Railway was altered about 1846, and that of the Dublin and Kingstown Railway in 1857, the alteration costing the latter company £38,000.


This unusual gauge is otherwise found only in the Australian states of Victoria, southern New South Wales (as part of Victoria’s rail network) and South Australia (where it was introduced by the Irish railway engineer F.W. Shields), and in Brazil.

Brief history of Irish railways

The Belfast & County Down Railway was just one of many railway companies in Ireland.

www.downrail.co.uk

 

[ThirteenArches]

And slightly off topic, have you noticed that 7ft (plus nothing) gauge is exactly 50% wider than 4 foot 8 (plus nothing)? One suspects a bit of hand- waving engineering by Isambard here.

 

[Rescars]

Crampton... can't resist posting this: Something wicked this way comes.... and just for fun, 4'10" gauge too.

If we are talking about a variation of a couple of inches, let's not forget the pioneering Scotch Gauge of 4ft 6ins, mainly to be found in Lanarkshire apart from the Lee Moor Tramway and the tramways of Tokyo.

 

[edwin_m]

If we are talking about a variation of a couple of inches, let's not forget the pioneering Scotch Gauge of 4ft 6ins, mainly to be found in Lanarkshire apart from the Lee Moor Tramway and the tramways of Tokyo.

And indeed the Glasgow tramways which were a bit narrower than standard so that rail wagons could run over them with their flange tips in the track grooves.