High-voltage cables installed in the disused Victorian railway tunnels in the 1960s, to bring new electricity supplies to the Manchester, UK area from power stations east of the Pennines area nearing the end of their operational life and are being replaced by National Grid (UK). The Woodland Tunnels comprise three adjacent ex-railway tunnels, each approximately 4,840 m (about three miles) long.

The tunnels formerly carried a Trans-Pennine rail link (commonly known as the Woodhead Route) from Manchester to Sheffield. The western entrances are at Woodhead in Derbyshire and the eastern entrances are at Dunford Bridge, near Penistone, South Yorkshire.

The decision to put cables in the tunnels rather than building new overhead power lines across the moors was made after representations to a public inquiry by the Peak Park Planning Board. The tunnels were bought by National Grid's predecessor organization, the Central Electricity Generating Board (CEGB), and are now owned by National Grid.

The Woodhead Tunnel cables form part of the 400-kV transmission system, which runs between National Grid's substations at Stalybridge, east of Manchester and Thorpe Marsh, near Doncaster.

At the time of their completion in 1845, the two Victorian tunnels were among the world's longest railway tunnels. British Rail added a third tunnel in 1953. The Victorian tunnels were acquired by the CEGB in the 1960s to carry the trans-Pennine 400-kV electricity link below ground, rather than over the moors of the Peak District National Park.

It is not possible to install new electricity cables alongside the existing cables in the Victorian tunnels for two reasons:

• Firstly, to ensure continued safe and secure electricity supplies for Greater Manchester, the existing cables need to remain in service while new cables are installed. Because of the confined space, there is not enough room to carry out major engineering works to install new cables in the tunnels alongside the existing "live" 400-kV cables.
• Secondly, despite a great deal of maintenance work over the years, the condition of the Victorian tunnels has continued to deteriorate and they would require considerable civil engineering works at substantial additional cost to be made safe for long-term use for any purpose.

Therefore the replacement cable circuits will be installed in the third, more modern, Woodhead Tunnel. This tunnel was closed in 1982 and was bought by National Grid in the early 1990s with this purpose in mind. This project forms part of National Grid’s ongoing national investment program and represents a significant investment in the region’s power network.

The new cables are being installed in the 1953 tunnel, via the entrance at Dunford Bridge, by the Electricity Alliance - East on behalf of National Grid.

Work began in February 2008 and will take approximately two years to complete. As the vast majority of the work takes place within the tunnel itself, the impact on the environment, the local community and visitors to the area is much less than that usually associated with major engineering works. However, some work is also required at the Woodhead tunnel entrance, the terminal pylons and the sealing end compounds at both ends of the tunnel.