Severn Bridge

The Severn Bridge (Welsh: Pont Hafren) is a suspension bridge spanning the River Severn between South Gloucestershire, just north of Bristol, England, and Monmouthshire in South Wales, via Beachley, a peninsula between the River Severn and River Wye estuary. It is the original Severn road crossing between England and Wales and took five years to construct at a cost of £8 million. It replaced the Aust ferry.

The bridge was opened on 8 September 1966, by Queen Elizabeth II, who hailed it as the dawn of a new economic era for South Wales. The bridge was granted Grade I listed status on 26 November 1999.

History

The first proposal for a bridge across the Severn, approximately in the same location as that eventually constructed, was in 1824 by Thomas Telford, who had been asked to advise on how to improve mail coach services between London and Wales. No action was taken, and over the next few decades the railways became the dominant mode of long-distance travel, with the Severn Railway Bridge at Sharpness being opened in 1879 and the main line Severn Tunnel in 1886. However, the growth of road traffic in the early 20th century led to further calls for improvements, and in the early 1920s Chepstow Urban District Council convened a meeting of neighbouring local authorities to consider a Severn crossing to ease congestion and delays on the A48 passing through the town. In 1935 Gloucestershire and Monmouthshire County Councils jointly promoted a Parliamentary Bill to obtain powers to build the bridge over the estuary, with 75% of costs to be met by the Ministry of Transport from the Road Fund. However, the Bill was rejected by Parliament after opposition from the Great Western Railway Company.

After World War II, plans began to be made for a nationally funded network of trunk roads, including a Severn Bridge, for which the contract was awarded to Mott, Hay and Anderson, with Freeman Fox and Partners. The public inquiry into the scheme was held on 24 September 1946 at Bristol university. However, because Government funding was prioritised for the similar Forth Road Bridge (opened in 1964), construction of the Severn Bridge was not started until 1961: the UK government announced in 1962 that construction costs would be 'recovered' by means of a toll of 2s 6d (GBP 0.125) on all vehicle crossings, though walking or cycling across the bridge would be charge-free. The substructure was completed by contractors John Howard and Co in 1963. The superstructure contract was awarded to Associated Bridge Builders Ltd in 1963, and completed in 1966. In parallel, the Wye Bridge was built by Cleveland Bridge & Engineering Company.

Component structures

The Severn Bridge crossing consists of four structures, which, listed in order from England to Wales, are: the Aust Viaduct, Severn Bridge, Beachley Viaduct and Wye Bridge. The Severn Bridge and Aust Viaduct was granted Grade I listed status on 26 November 1999, while the Wye Bridge and Beachley Viaduct was granted Grade II listed status on 29 May 1998.

Aust Viaduct

The Aust Viaduct is a twin box girder structure with a concrete deck, which carries the roadway from the top of Aust Cliff to the first gravity anchorage of the old Severn Bridge. The roadway is then carried over the top of the concrete anchorage to the Severn Bridge.

Severn Bridge

The Severn Bridge is located close to the former Aust Ferry. The bridge is a suspension bridge of conventional design, with the deck supported by two main cables slung between two steel towers. In 1966 the cables supporting the bridge deck were spun from 18,000 miles (29,000 km) of wire. An unusual feature of the suspension cables carrying the deck is that they are not vertical, as for most suspension bridges, but rather arranged in a zig-zag fashion, with adjacent mounts closely spaced. The triangulation this offers is an attempt to reduce vibration, as is the prominent use of Stockbridge dampers on the cables. The bridge is 5,240 ft (1,600 m) long, consisting of a 3,240 ft (988 m) central span between the towers and the two 1,000 ft (305 m) side spans. The towers rise to 445 ft (136 m) above mean high water and are of hollow box construction. The deck is an orthotropic steel box girder of aerofoil shape with cantilevered cycle tracks and footway supported from the box. The shape of the bridge was determined by the designers Freeman, Fox and Partners following wind tunnel tests for the Forth Road Bridge, after the original wind tunnel model was accidentally destroyed. The sections of the deck were built at Fairfield-Mabey in Chepstow, and each 132 tonne section was then floated down the river before being hoisted into position. The construction was undertaken by Sir William Arrol & Co. and completed in 1966.

Beachley Viaduct

The Beachley Viaduct is also of similar box girder construction as the Severn Bridge but is supported on steel trestles as it crosses the Beachley peninsula. The peninsula contains an army camp, which the bridge crosses.

Wye Bridge

The Wye Bridge is a 1,340 ft (408 m) long cable-stayed bridge, which crosses the border marked by the River Wye between England and Wales, 2 miles (3.2 km) south of Chepstow. It consists of a single large cable stayed section with two single-leg pylons supporting the bridge deck from the centre of the roadway. The deck is an orthotropic box girder similar to the Severn Bridge but has a different appearance as it has two sets of cable stays on each of two towers. Originally there was only one set of cable stays but these were replaced during the strengthening works.

Post-construction changes

In January 1977, it was announced that bridge traffic would be restricted to a single lane in each direction following the discovery of several weaknesses in the ten year old structure. The lane closures would last for several months.

The Severn Bridge crossing was strengthened and resurfaced in the late 1980s as the weight of traffic grew. The work included the strengthening of the Severn Bridge towers and deck, an extension to the existing Wye Bridge towers and the replacement of the original single stays with two stays. The open structure of the new stays is designed to facilitate maintenance. Most of the strengthening work was inside the deck box and towers and so is not visible. The surfacing is a 35 mm (1.4 in) thick layer of mastic asphalt over an acrylic waterproofing membrane.

The road is only two carriageways of two lanes in each direction, and as traffic volumes grew it became a major bottleneck. At its peak, it was carrying 50,000 vehicles a day. The burden of maintenance also became unmanageable, so that by the 1990s a second bridge was necessary. Since the construction of the Second Severn Crossing, the original crossing carries 15,000 vehicles day, 25% of the total traffic traversing the estuary.

Tolls

Shortly after the opening of the Severn Bridge, Anglo-Welsh poet Harri Webb wrote an Ode on the Severn Bridge:

The toll is indeed collected on the English side, and only on vehicles travelling westwards from England to Wales, leading some people to describe it as a "tax on entering Wales", both in jest, and also as a more serious anti-toll campaign. Originally, tolls were charged in both directions, but the arrangements were changed in the early 1990s to eliminate the need for a set of toll booths for each direction of travel and the potential for traffic waiting to pay the toll backing up onto the bridge itself.

In 1966 the toll for using the new motorway crossing was set at 2s 6d (post-decimalisation equivalent £0.125) for all vehicles apart from solo motorcycles which enjoyed a reduced toll of 1s (£0.05). For a small car the bridge toll represented a saving of 7s (£0.35) on the price, at that time 9s 6d (£0.475), of using the ferry crossing. By 1989, the toll had reached £2 each way for goods vehicle having an unladen weight exceeding 1.525 tonnes and passenger vehicles adapted to carry more than 16 passengers and £1 each way for other vehicles. Currency depreciation has been a feature of UK monetary policy in the intervening decades, and the RPI is a widely applied surrogate for the resulting impact of general price inflation: if the Severn toll had increased in line with general inflation since September 1966, when the British Queen opened the bridge, the original value of £0.125 would have reached £2.02 each way in January 2010.

As of January 2011, the toll is £5.70 for a car, increasing to £17.20 for a heavy goods vehicle.Motorcycles and disabled badge holders are exempt from the tolls, although both must stop at the toll booths to have their eligibility confirmed, and also to allow the barrier to be raised. The tolls for the Second Severn Crossing are the same, although in that case, the tolls are collected on the Welsh side (although still for traffic entering Wales, not leaving it), sufficiently far from the bridge that even severe queueing doesn't reach it. A system known as the Severn TAG made by Amtech is also in operation, which allows drivers to pay electronically without having to stop at the toll booths. TAGs are available either on a per-trip or a seasonal basis, although only the latter attracts a discount.

Credit/debit cards are not accepted on either bridge. However, drivers who do not have the means to pay are able to get a bill from the toll operator and pay by post later. In June 2010, Norman Baker, the Parliamentary Under-Secretary of State for Transport, stated that cards would be accepted in time for the 2010 Ryder Cup in October. In September 2010, the Highways Agency announced that a temporary system for accepting card payments would be in place for the Ryder Cup from 27 September to 3 October 2010. However, users would be required to enter their PIN and cash was still the recommended payment method to avoid delays. A permanent card payment system which will not require a PIN should be ready early in 2011.

The cycle path and footpath, which run along either side of the roadway, may be used free of charge. Only the original bridge has such a public access.

Historic overview of the toll charges
40 year inspections

During its 40th year of operation, the bridge was inspected to check for corrosion of the suspension cables. According to the Highways Agency, the inspection concluded that the bridge needed restrictions on heavy goods vehicles. Such vehicles are now restricted to one lane on the bridge, with weight restriction signs in place. A system of installing a rubber casing on the cables with dry air circulation is to be used on the Forth Road Bridge and a similar system may be implemented on the Severn Bridge, in a move to halt the progress of the corrosion.

Simultaneous closures in 2009

On 6 February 2009, during a week of snowfall throughout Britain, both Severn bridges were closed simultaneously due to ice falling from the bridge structure and damaging vehicles. On 22 December 2009 both bridges were closed again for the same reason.

This was only the third time that both bridges have been closed together, the first being due to a chemical fire in Avonmouth some years earlier.

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