The Dartford bridge across the river Thames is being built to ease traffic congestion on the M25. It will be Europe's longest cable-stayed bridge, with four lanes for southbound traffic. The construction is led by Trafalgar House plc and involves complex design work for the main piers to withstand ship impacts. The project is progressing well, with the transportation of reinforced concrete caissons from Rotterdam being a key milestone. Each construction stage is moving towards the center of the bridge, aiming for completion in early 1991.