Network Rail’s orange army will be transforming the 130-year-old Severn and Patchway tunnels this autumn in preparation for the arrival of a new fleet of longer, faster, quieter and greener electric trains.

The work forms part of Network Rail’s £40bn Railway Upgrade Plan to provide a bigger, better, more reliable railway for passengers and follows projects already underway in Bristol, Bath, Swindon, Didcot and Oxford to electrify the Great Western Main Line.

Communication with passengers about the disruption to their journeys is already taking place with emails sent to over one million season ticket holders and an intensive programme of leafleting, in-station advertising and announcements planned.

The work required to prepare both tunnels for electrification is extensive and will involve installing conductor beams to power the new fleet of electric trains to run underneath. To install this beam in the Severn tunnel, four tonnes of soot needs to be removed and extensive improvements made to the brick work.

The scale of this engineering challenge together with the type of machinery required to carry out the work means that a temporary closure of both tunnels is unavoidable. This temporary closure will take place over six weeks, from 12 September to 21 October 2016.

Mark Langman, Network Rail’s managing director for the Western route, said: “Electrification has many long-term benefits including faster, more frequent trains and a boost to economic growth in towns and cities across the whole of the Western route and beyond.

“I’d like to thank passengers in advance for their patience and understanding while we deliver the essential upgrades needed to prepare these tunnels for electrification and the benefits this will bring.

“Throughout the work, the Great Western route will remain open but we are urging people to check before they travel. Some journeys, especially those in and out of Wales, will take longer and a bus replacement service will be in operation in some cases.”

Rob Mullen, Great Western Railway’s general manager central, said: "The electrification of the two tunnels is a vital part of the modernisation of the railway between the south west, Wales and London; and once complete will enable us to deliver more frequent services, more seats, and to reduce journey times.

"Electrification will also deliver a greener and quieter railway, resulting in cleaner air and a reduction in noise for those living near the railway.

“We would like to thank our passengers in advance for their understanding and patience as this vital work is conducted."

Over the next six months, Network Rail and Great Western Railway will continue with their extensive engagement programme to ensure passengers can make informed travel choices during the temporary closure.

Ahead of the closure, passengers are advised to check before they travel by visiting train operators’ websites, by visiting www.GWR.com/severntunnel2016 or via National Rail Enquiries.

Updates will also be available on Twitter via @networkrailwest and @gwrhelp.