The Dartford Tunnel is a road tunnel located in Dartford, Kent, England. It runs beneath the River Thames and connects the A2 and M25 motorways. Opened in 1963, the tunnel consists of two separate tunnels, one for northbound traffic and the other for southbound traffic, allowing for efficient vehicle movement across the river. The tunnel is a vital part of the UK's transport infrastructure, facilitating the movement of goods and commuters. It is subject to a toll, which helps fund maintenance and improvements. The Dartford Crossing, which includes the tunnel and the Dartford Bridge, is one of the busiest river crossings in the country.