The Dartford - Thurrock River Crossing, Dartford River Crossing (DRC) (or simply the Dartford Crossing) is a major road crossing of the River Thames in England, connecting Dartford in the south to Thurrock in the north, via two road tunnels and the Queen Elizabeth II Bridge. It opened in stages, the west tunnel on 18 November 1963, the east tunnel in 1980, and the bridge in 1991. Until the opening of the bridge, built to the east of the two tunnels, the crossing was known as the Dartford Tunnel.
More information on the Wikipedia page [1]
Details of paying the Dart Charge for using the bridge are TfL and GOV.UK