A two-year renewal of infrastructure on the two-mile long Sevenoaks tunnel in South East England is giving passengers a reduction in delays and faster journeys. The tunnel has been given a £21 million refurbishment which included the replacement of thousands of sleepers, the laying of several miles of new track and the installation of new drainage systems.

The work on the 150 year-old tunnel began in 2017 and has included partially lining 13 ventilation shafts measuring up to 120 metres deep below the Sevenoaks Weald which has stopped water flooding the tracks below and causing delays. Engineers have also overhauled its electrical systems to make them more reliable and ensure that other lines in the area can operate if there’s a power issue in the tunnel.

The work will improve reliability for Southeastern as well as Thameslink services, which are affected by knock-on delays and congestion when Southeastern’s London services need to be diverted.

The team have employed several innovations during the project, including 3D modelling to prove the suitability of special padded sleepers for reducing stress to the Victorian structure and enabling faster train speeds, while safe access methods have allowed the tunnel to stay open during most of the works to the ventilation shafts, where previously line closures would have been required.

Journeys through the Sevenoaks tunnel are now smoother and faster now that the work has allowed speed restrictions to be removed with trains able to travel at up to 90mph instead of 50mph.

“We’re very pleased that this major work on the Sevenoaks Tunnel has been carried out and will improve the reliability of services for our passengers. I’d like to thank passengers for their patience during the 15 weekend closures of the line which have been necessary to allow this work to be carried out,” said Ellie Burrows, Southeastern’s train services director.

The project has been a major element of a £300 million government-funded programme to tackle delay hotspots and improve railway reliability for the new Thameslink timetable.