IN Brief:
- Network Rail will replace ageing points, install track and upgrade overhead line equipment at Dolphin Junction.
- A preparatory closure is scheduled for 28–29 November, followed by major works from 25 December to 3 January.
- Great Western Railway services are expected to return to London Paddington on 4 January 2027.
Network Rail is preparing a £27.8m renewal of Dolphin Junction near Slough, replacing ageing points, modifying the track layout and upgrading overhead line equipment on the Great Western Main Line. The programme will require a two-day closure in November, followed by major engineering works over Christmas and New Year. The improvements are intended to reduce congestion and improve reliability on the western approach to London Paddington, where trains serving the Thames Valley, South West and Wales share heavily used infrastructure.
The junction provides connections between different running lines, allowing trains to move between routes as they approach or leave the capital. Its operating importance creates a particular challenge for infrastructure renewal because substantial construction work requires the affected tracks to be taken out of service. Network Rail has consequently planned the most disruptive activities around extended railway possessions, with alternative journeys being arranged for passengers.
The investment includes replacement of points and improvements to the track configuration, together with the installation of new track. Points contain movable rail components that direct trains between different routes. Their position, alignment and condition are important to safe operation, particularly at junctions where numerous movements take place throughout the day. Wear and deterioration can increase maintenance requirements and, where faults develop, restrict the availability of the railway.
Network Rail expects the revised layout to allow trains to move through Dolphin Junction more efficiently. The changes are intended to address congestion associated with the existing arrangement, although the organisation has not published a quantified forecast of journey time savings or the number of infrastructure failures expected to be prevented. The £27.8m figure covers the announced investment rather than an identified individual contractor’s award.
Overhead line equipment will also be upgraded as part of the works. Electrified trains draw power through contact between their pantographs and wires supported above the track. Where tracks diverge, the overhead equipment must be positioned to maintain the required relationship with the train and the route it follows. Track alterations and electrical infrastructure therefore need to be coordinated during the renewal, with testing required before the affected sections return to normal operation.
The first major possession is scheduled for Saturday 28 and Sunday 29 November, when lines to and from Paddington will close. This period will allow preparatory activities to be undertaken before the longer Christmas programme. The principal closure is planned from Christmas Day until Sunday 3 January, inclusive, incorporating the period when the national railway would ordinarily have reduced or suspended services for the Christmas holiday.
Great Western Railway services will be particularly affected by the closure of access to Paddington. Some trains will begin and terminate at Reading, while others will use a diversionary route to London Euston. Connections through Waterloo and Marylebone will also be available, although the suitability of individual alternatives will depend on the passenger’s origin and destination.
The arrangements are not uniform across all operators. Elizabeth line and Heathrow Express passengers are being advised to check their journeys separately, with services on those routes expected to begin returning from New Year’s Eve. Great Western Railway is scheduled to regain access to Paddington on Monday 4 January. The timing reflects the planned engineering programme and associated operational arrangements, rather than a guarantee that every individual service will operate normally throughout the period.
The junction works form part of a wider programme of engineering investment across the Thames Valley. Network Rail also intends to undertake a deep clean of Paddington station during the disruption. That activity is separate from replacing the junction infrastructure at Slough, although both are being coordinated within the wider period of altered operations.
Delivering a track renewal at an operational junction requires the existing infrastructure to be removed, replacement components installed and the finished arrangement checked before it can safely carry trains. The construction sequence must accommodate the relationship between track geometry, points, electrical equipment and the railway’s operating systems. Network Rail has not published the number of points assemblies being replaced or the detailed installation method, so neither can be attributed to a particular supplier or contractor at this stage.
The work will also affect freight movements using the Great Western route. Railway possessions must account for the needs of passenger and freight operators, particularly where diversions or revised schedules are required. Network Rail has acknowledged the short-term disruption for both groups while identifying reduced congestion and improved reliability as the intended longer-term outcomes.
The physical constraints of the junction help explain the use of an extended possession. Replacing isolated components during shorter overnight engineering windows can be appropriate for some maintenance activities, but a larger track configuration change requires coordinated access across the affected infrastructure. The announced closures provide time for work on several related assets, although the detailed allocation of activities between November and the Christmas period has not been published.
Network Rail has previously undertaken performance improvement work on the Great Western route, with further investment intended to reduce disruption associated with ageing infrastructure. Dolphin Junction is one of the locations where the organisation is now committing substantial renewal expenditure. The eventual effect on railway performance will depend on the commissioned assets and their operation after completion, rather than the investment value alone.
Journey planners have been updated with information through 4 January, enabling passengers to review the available services before travelling. The immediate milestones are the November possession and the main Christmas engineering programme. Subject to the planned works being completed and the railway returning safely to service, Great Western Railway trains are expected to resume access to Paddington on 4 January 2027.
