Prince of Wales Bridge

The Prince of Wales Bridge (Welsh: Pont Tywysog Cymru), previously the Second Severn Crossing (Welsh: Ail Groesfan Hafren) until July 2018, is the M4 motorway bridge over the River Severn between England and Wales, opened in 1996 to supplement the traffic capacity of the Severn Bridge built in 1966. The bridge is operated by England's National Highways. It has a total length of 5,128 metres (16,824 ft). 3.2 miles.

It is southwest of the Severn Bridge and because it is more closely in line with the rest of the M4, it reduces the length of the journey between England and Wales. The junctions at each end are designed for most traffic to use this crossing, and in order to use the old Severn Bridge, one has to leave the M4 at junction 21 and join the M48 near Aust or at junction 23 near Magor. The new crossing carries more traffic than the Severn Bridge, which is still in use. It is wider than the Severn Bridge, having three lanes and a narrow hard shoulder each way, compared to the two lanes, cycle path and narrow footpath of the original crossing. It is a cable-stayed bridge, whereas the Severn Bridge is a suspension bridge. The position of the bridge is close to that of the Severn Tunnel, which has carried the railway line beneath the river bed since 1886.

Much of the estuary is mudflats at low tide, but at high tide these can be covered by as much as 14 metres (46 ft) of water. This presented the engineers with a constraint: packets of work were scheduled at low tide, and needed to be completed within the short windows allowed by the tides.

The concession given to the consortium which financed, built and operate the bridge required them to take over the outstanding debt on the original Severn Bridge and to operate the two bridges as a single entity. Tolls were set annually by the government based on the previous year's change in the Retail Price Index. On the expiry of the concession in January 2018, the consortium was required to hand the bridge over to public ownership. The tolls on both bridges were subsequently scrapped in December 2018.

The Severn Estuary presented a barrier between the Bristol area and South Wales. The estuary has a maximum tidal range of 14.5 metres (48 ft), amongst the highest in the world, and during a rising or falling tide there are strong currents of up to 8 knots (4.1 m/s). Much of the estuary is mud flats that are exposed at low tide; these have been designated a Special Protection Area. The central part of the estuary is a navigable channel which, at the site of the bridge, is known as "The Shoots". The bridge is upstream from Avonmouth and the Port of Bristol, but downstream from the Port of Sharpness. The Gloucester Harbour Trustees have responsibility for controlling navigation in the estuary's tidal waters upstream from the bridge.

Until 1966, road travellers could either use the Aust Ferry, which had operated since medieval times (and as a car ferry since 1926), or use the scheduled car shuttle train service through the Severn Tunnel between Pilning and Severn Tunnel Junction, which operated from 1926 until 1966. Otherwise, the detour via Gloucester would add 57 miles (92 km) to the journey. In 1966, the first Severn road bridge, a four-lane suspension bridge, was opened, carrying the M4 motorway between England and South Wales. By 1984, traffic across the first Severn Bridge had tripled and it was projected that by the mid-1990s, the old bridge would be running at capacity. A study was commissioned into building either a second bridge or a tunnel. The consultants reported back in 1986, recommending that a new bridge be built downstream from the existing bridge.

In 1988, it was announced that tenders would be invited from private consortia to fund, build and operate the bridge for a specified period. The consortium would also take over the management of the old bridge and the associated £100 million debt. Tenders were invited in 1989; and in 1990 the concession to build the bridge was awarded to Severn River Crossing plc. Construction work started on 26 April 1992 and the bridge was opened by Prince Charles (the future Charles III, then the Prince of Wales), on 5 June 1996.

The chief architect of the bridge was Ronald Weeks of the Cardiff-based Percy Thomas Partnership, with the detailed engineering design by the Halcrow Group and the French consultancy SEEE [fr]. The bridge has portals close to Sudbrook, Monmouthshire on the Welsh side and Severn Beach in South Gloucestershire on the English side. It has three principal sections – a 25 span viaduct on the English side of length 2,103 m (6,900 ft; 1.307 mi), a 24 span viaduct of length 2,077 m (6,814 ft; 1.291 mi) on the Welsh side and the bridge itself, a 948 m (3,110 ft; 0.589 mi) structure with a 37 m (121 ft) navigational clearance, giving a total length of 5,128 m (16,824 ft; 3.186 mi). The central section, called the Shoots Bridge, is of cable-stayed design and the central span (between the bridge pylons) is 456 metres (1,496 ft) in length. The approach viaducts are of a segmental bridge design. The crossing forms a very slight reverse "S" curve – the roadway has an approximate east–west alignment at each of the portals, while the central bridge follows an alignment approximately WNW to ESE.