The Medway Tunnel is a tunnel under the River Medway linking Strood with Chatham in Kent, England. It forms part of the A289 Medway Towns Northern Relief Road. The Medway Tunnel is the first immersed tube tunnel to be built in England and only the second of this type in the UK, the other at Conwy, North Wales.

The Rochester Bridge had been the lowest river crossing of the River Medway for centuries, and despite expansion in the 1970s was very congested. In the late 1980s, the Medway Tunnel was proposed downstream of the Bridge to relieve congestion on the bridge, to allow greater access to the Medway Towns and assist with redevelopment of Chatham Dockyard.

Medway Tunnel Act 1990
Act of Parliament
Parliament of the United Kingdom
Long title	An Act to authorise the Wardens and Assistants of Rochester Bridge in the county of Kent to construct works and to acquire lands; and for other purposes.
Citation	1990 c. xxii
Dates
Royal assent	26 July 1990
Text of statute as originally enacted

The Medway Tunnel Bill – promoted by the Rochester Bridge Trust – was submitted to Parliament in 1988. The Medway Tunnel Act 1990 (c. xxii) was passed granting the Rochester Bridge Trust the power to build and own the tunnel.

The £80m project was carried out by an HBM Civil Engineering / Tarmac Construction joint venture, and started in May 1992. The tunnel itself was constructed in three distinct sections. The central part of the tunnel is the 370 metres (1,210 ft) of immersed tube, which is linked to cut and cover tunnels on both the Strood and Chatham banks of the river, with a total tunnel length of 720 metres (2,360 ft).

As part of the construction project, 800 metres (2,600 ft) of new dual carriageway and a new junction was built to connect the new tunnel to the existing road network. Separate from the project, various bypasses and link roads were constructed to provide access to the local area - the A289 Medway Northern Relief Road.

The Medway Tunnel was officially opened by the Princess Royal on 12 June 1996. In 1996, it won an award from the UK's Concrete Society.

In 2008 negotiations were completed by Medway Council which purchased the freehold of the tunnel from the Trust for £1 with a £3.6m contribution on future costs.

As of March 2023, the tunnel is used by around 40,000 vehicles per day.

Cyclists are currently not allowed to travel through the tunnel which is not part of the local cycle network.

• Rochester Bridge Trust