GWR proves Brunel’s sunshine theory Is there light at the end of Brunel’s Box Tunnel?

Monday 10th April 2017

On Sunday 9 April, a date that marked Brunel’s 211th birthday, a team of Great Western Railway (GWR) engineers took to the track to test one of the most enduring theories surrounding Brunel’s iconic Box tunnel just outside of Bath.

It is believed that Brunel deliberately designed the two mile-long Box Tunnel so that every year on his birthday the rising sun would shine directly through from one end to the other, creating an astonishing effect.

Engineers and mathematicians have previously concluded that the theory could hold true with the calculations published in the New Civil Engineer and elsewhere.

True to the genius of Brunel, the tunnel does in fact align with the rising sun, which lit up a significant section of the tunnel, but despite beautiful conditions on Sunday morning, it did not make it all the way through to the end. 

GWR Commercial Development Director Matthew Golton said:

“The alignment of the sun directly between the tracks makes it difficult to imagine it wasn’t engineered. Given that the sun rises in a slightly different spot from the east each day it’s hard to predict the days with pinpoint accuracy.

“That said, Brunel might have calculated it right – when building the tunnel his calculations were so accurate that when the two ends joined up it was only 5cm out – but he may not have taken into account leap years and so the sun effect has moved away from the actual day of his birthday. Take a look at the photos and draw your own conclusions.”

Yesterday was the last opportunity for track access to test the sunlight theory before new Intercity Express Trains begin operating on the line later this year. The investment into electrification marks the most significant change since diesel replaced steam half a century ago.

Notes to editors

Great Western Railway (GWR) provides high speed, commuter, regional and branch line train services. We help over 100 million passengers reach their destinations every year - across South Wales, the West Country, the Cotswolds, and large parts of Southern England.

We’re currently seeing the biggest investment in the network since Brunel so we can offer more trains, more seats, and shorter, more frequent journeys and continue the network’s heritage of helping connect more businesses to new and prosperous markets. Through a series of initiatives we aim to be a good neighbour to the communities we serve and are committed to making a positive social impact in those regions. Learn how we're Building a Greater West at GWR is a FirstGroup company.