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M4 motorway bridge over the Severn Estuary in the United Kingdom

The Second Severn Crossing (Ail Groesfan Hafren), officially named the Prince of Wales Bridge (Pont Tywysog Cymru) since 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
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 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 , amongst the highest in the world, and during a rising or falling tide there are strong currents of up to 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 mile (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 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 , a 24 span viaduct of length on the Welsh side and the bridge itself, a structure with a navigational clearance, giving a total length of The central section, called the Shoots Bridge, is of cable stayed design and the central span (between the bridge pylons) is 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. The Severn Railway Tunnel passes under the estuary bed on a line which is generally about upstream of the bridge, but which passes under the line of the bridge close to the English shore. The deck, which carries three lanes of traffic in each direction, is wide. The sides of the bridge are fitted with baffle plates to reduce lateral wind loads coming from the Severn Estuary onto the traffic; this has reduced the number of times that speed restrictions have been needed. The overall design of the new crossing makes it more resistant to high winds than the old Severn Bridge. and is used for safe access to ten stations, such as lifts inside the cable pylons, for bridge maintenance. It can carry up to four passengers plus two tonnes of equipment in its trailer, with an integral crane and safety features such as interlocks, emergency battery propulsion capable of returning to either end of the crossing, and a dead man's switch. During the 1990s and early 2000s, the Rapid Access Train was initially disused for a number of years due to rail faults, but has subsequently been returned to service. Travelling access gantries are also present underneath each segment of the crossing to allow for inspection and maintenance across the full width of the structure, with hydraulic lift platforms capable of reaching multiple levels. This company also took over the responsibility of managing and maintaining the old Severn Bridge crossing, as well as managing and maintaining the new crossing. The cost of constructing the new crossing was to be paid for by tolls collected from motorists using the two crossings. Work on the new crossing began in 1992. Completion was in 1996. Sub assemblies for the bridge were constructed onshore and then shifted by a large tracked vehicle (similar to that used to move the Apollo and Space Shuttle at Cape Kennedy) onto a barge (the SAR3), prior to being floated out on the high tide to the site. The 37 bridge pier foundations on the approach viaducts are apart, and consist of open concrete caissons weighing up to 2,000 tonnes, which were founded on the rock of the estuary bed. The decking consists of post stressed match cast sections, weighing each. In 1988, the Severn Estuary was designated a Special Protection Area. The same year an area of 99 km2 (38 sq miles) was notified as a Site of Special Scientific Interest and designated as such the following year; in 1995, this was extended to cover the whole of the Ramsar site. Prior to the bridge's construction, environmentalists raised numerous concerns and criticisms, chiefly about the immediate damage from construction work and the effects of long term pollution from a projected increase in car traffic. The construction process resulted in a temporary increase in turbidity of the Severn waters. Although eelgrass is reasonably tolerant to short term high turbidity and consequent loss of light, the bed of eelgrass in the river was observed to decline considerably during the period of construction. The construction of the approach roads and toll plaza resulted in the permanent loss of some wet pastureland. Field surveys carried out in 2003 and 2004 reported that the bridge had little effect on the flight paths of the various birdsit was noted that when curlews, dunlins and lapwings approached the bridge, they would change course to gain height and fly over the bridge, but that oystercatchers and turnstones would fly under the bridge. The surveys also showed that the bridge had minimal impact on the roosting habits of most birds, though a flock of mallards were seen to be roosting directly under the bridge, with many positioning themselves on the dry concrete base on one of the pillars. Likewise, it was noted that the bridge had little impact on the birds' feeding habitsturnstones and lapwings were recorded as feeding on mudflats directly under the bridge while the absence of other waders was attributed to the rocky nature of the foreshore. and is now managed by National Highways.

Tolls were collected from westbound traffic only, near Rogiet, 2 mile (3 km) in Wales. In late 2008, UK VAT was reduced from 17.5% to 15%, but the bridge toll remained unchanged. For convenience the tolls were kept at round multiples of 10p (the bridge toll was largely paid in cash as card payments were not accepted until mid 2012), but the 13p VAT reduction was not passed on immediately. In 2009, the planned toll for cars would have been £5.50, as the announcements listed,

In the 2016 United Kingdom budget, Osborne announced that toll charges on the Severn crossings would be halved in 2018. However, in July 2017 it was announced that the toll would be abolished,
In July 2017, the Welsh Secretary, Alun Cairns, announced that tolls would be scrapped at the end of 2018, claiming that this would boost the South Wales economy by around £100m a year.

The toll levied was always identical to that on the Severn Bridge. Toll categoryDescriptionCategory 1Cars and minibuses with up to 9 seatsCategory 2Small buses with up to 17 seatsVans up to 3.5 tonnesDouble cab pickup trucksCategory 3Buses with more than 17 seatsGoods vehicles weighing 3.5 tonnes or more

DateCategory 1Category 2Category 35 June 1996£3.80£7.70£11.501 January 1997£3.90£7.80£11.701 January 1998£4.00£8.10£12.101 January 1999£4.20£8.40£12.501 January 2000£4.20£8.50£12.701 January 2001£4.40£8.70£13.101 January 2002£4.40£8.90£13.301 January 2003£4.50£9.00£13.501 January 2004£4.60£9.30£13.901 January 2005£4.80£9.60£14.301 January 2006£4.90£9.80£14.701 January 2007£5.10£10.20£15.301 January 2008£5.30£10.60£15.901 January 2009£5.40£10.90£16.301 January 2010£6.00£12.10£18.101 January 2013£6.20£12.40£18.601 January 2014£6.40£12.80£19.201 January 2015£6.50£13.10£19.601 January 2016£6.60£13.20£19.801 January 2017£6.70£13.40£20.008 January 2018Free

On 6 February 2009, the bridge was closed due to bad weather for the first time since its opening, after a number of vehicles were hit by falling ice. Bad weather, and again falling ice, repeated this in December 2009. Temporary speed limits are put in place due to high winds or thick fog, with drivers informed by the electronic signs. Because of the more advanced aerodynamic design of the later bridge, the Second Crossing is far less prone to such restrictions caused by crosswinds than the first Severn Bridge. On 18 February 2022, both the Prince of Wales Bridge and the Severn Bridge were closed during Storm Eunice, due to high winds. It was the first time that the Prince of Wales Bridge had been closed because of winds.

On 5 April 2018, the Secretary of State for Wales, Alun Cairns, announced that the crossing would be renamed as the Prince of Wales Bridge at a ceremony later in the year. He said that the renaming would be "a fitting tribute to His Royal Highness in a year that sees him mark 60 years as The Prince of Wales and decades of continued, dedicated service to our nation". An online petition, heavily shared via social media, against the renaming had received more than 30,000 signatures by 8 April. Some politicians criticised the proposed renaming and the lack of public consultation on it, but it was confirmed that the First Minister of Wales, Carwyn Jones, had raised no objection to the proposal. The bridge was formally renamed on 2 July 2018 where a plaque was unveiled by the Prince and the Duchess of Cornwall, which was followed by a reception for local dignitaries and business leaders at the nearby Celtic Manor Resort. There was no prior press release or other official communication from either the UK or Welsh Governments. The total cost for renaming the bridge, including the installation of two above road signs (and associated staffing costs to close the carriageways with and traffic diverted via the M48) along with the ceremony was £216,513.39.