Snowdon Mountain Railway Gradients

It is often said that the SMR experience is similar to being on a Swiss mountain line. Certainly for those who can’t or do not want to travel abroad, Snowdonia is the nearest in the UK one can get a sense of the Swiss Alps, with its deep valleys and numerous narrow gauge railways.

The SMR actually takes the easiest route to Snowdon and thus does not have gradients as severe as those found on many Swiss lines, neither is it as steep as the nearby Great Orme’s maximum of 1 in 3.8, nor the many steep inclines at Dinorwig and other slate quarries in Snowdonia.

The SMR just manages to beat the Great Orme in terms of how much altitude is achieved in one mile. The Great Orme’s steeply graded lower section climbs 400ft with an average of 1 in 6.6 whilst the SMR does slightly better on its Clogwyn-Summit section at an average of 1 in 6.5.

We shall look at the gradient data for the SMR and analyse what these mean.

The average gradients on the SMR are something like this:

Llanberis – Hebron; 1 in 8.5

Hebron – Halfway; 1 in 10.7

Halfway – Clogwyn; 1 in 6.7

Clogwyn – Snowdon; 1 in 6.5

From the figures it can be seen that the lower half of the line is quite generous whilst the upper half rises more steeply. Indeed the lower section rises barely two thirds of the total of the upper section. The heights attained are as follows:

Llanberis – Halfway; 1288ft

Halfway – Summit; 1852ft


The line’s switchback nature from a point above Cader Ellyll bridge looking down towards Waterfall station


A close up along the flatter section between Hebron and Halfway with its lengthy sections of flat gradient. The furthest section is 1 in 13.2, the middle bit is 1 in 7.3 and the nearest 1 in 8. The rise from Hebron station to the start of the curve in the foreground is around 350ft.

The Hebron to Halfway section’s average gradient is very generous at 1 in 10.7 but manages many steeper gradients than the Llanberis to Hebron section.


Gradients between Tryfan Bridge and the halfway ascent point of the line.

To attain the rise to Halfway station, the railway has to tackle much shorter, steeper, gradients.


The halving of each section means one never quite gets there…Zeno’s paradox doesnt quite describe the SMR but there’s still this: Two trains shown here passing are not even halfway up the mountain for that ‘halfway’ is still half a mile upwards of Halfway station!

In the previous section on the railway’s bridges I mentioned Halfway is a misnomer in terms of how much height has been gained. Despite being the equidistant point, its just three eighths of the total height, and preceedes the greater part of the climb.


Curves and gradients below Clogwyn

As built the railway has to climb 915ft from Halfway to Clogwyn, involving many steeper sections. Compared to the lower half of the line, longer sections of near maximum gradient have to be used. Most of this section averages 1 in 6.7, given that several lengths are at 1 in 6.6 and a long one at 1 in 6. This latter is the SMR’s longest continous gradient almost half a mile.


Gradients below and above Clogwyn. No.4 Snowdon and carriage descend the 1 in 5.5 on Clogwyn Goch en route to Llanberis.

The SMR is billed as having maximum gradients of 1 in 5.5. This is achieved over two sections on the final part from Clogwyn to the Summit. Immediately the train has crossed the Clogwyn ridge, the first 1 in 5.5 section is met which passes over the top of the Clogwyn cliffs. Its a third of a mile in length and the second longest continous gradient on the line.


The final 1 in 5 stretch leading up to Hafod Eryri/Summit station

The line then eases back to 13.2 briefly before another 6.6 section.The broad mountain shoulder approaching Bwlch Glas allows the trains to take a breather at 1 in 15, before tackling a 6.6 and the second 5.5 up the steeply graded north east shoulder of Snowdon to its summit station. The total climb from Clogwyn is 937ft.


Gradient profile adapted from that published in ‘Snowdon Mountain Railway’ (1969)

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