Lower Thames Crossing. The Lower Thames Crossing will be a new road crossing connecting Kent, Thurrock and Essex. Approximately 14.5 miles (23km) in length, it will connect to the existing road network from the A2/M2 to the M25 with two tunnels (one southbound and one northbound) running beneath the River Thames. The scheme also includes improvements to the M25, A2 and A13, where the scheme connects to the road network, new structures and changes to existing ones (including bridges, buildings, tunnel entrances, viaducts, and utilities such as electricity pylons) along the length of the new road and a free-flow charging system through the tunnel.