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Severn Bridges History

There are two main bridges across the Severn, the ‘Severn Bridge’ and the ‘Second Severn Crossing’, with the latter being the last point of the River Severn as it then becomes the Severn Estuary as it travels towards the open sea in a south westerly direction.

These bridges have been best known for carrying the M4 motorway, a route that connects London with south Wales. Indeed, upon opening, Queen Elizabeth II hailed it as the dawn of a new economic era for the area. She opened the Severn Bridge on 8th September 1966 and until that time, traffic had for centuries relied on the Aust ferry, a service that had crossed the river from Aust Cliff on the English side to Beachley Peninsula on the west side. It’s believed to have been the point at which Roman legions were ferried across, and it was certainly chronicled by the monks who travelled to nearby Tintern Abbey in the 12th century.

The idea of a bridge, whilst probably conceived many years earlier, was first seriously proposed in 1824 by Thomas Telford. This being part of his commissioned study and recommendation for improving the mail coach service between England and Wales. Economic pressure saw the opening of the Severn Rail Bridge in 1879 and the Severn Rail Tunnel in 1886, but quite remarkably, no road bridge was built for another 80 years.

An enquiry was held into the viability in 1946, and whilst agreed, it was felt that funds available should first be channelled towards the Forth Bridge in Scotland.

Work started in 1961 and it took five years to build, costing £8 million. The consulting engineers were Messrs Mott, Hay & Anderson and Freeman Fox & Partners. The substructure was contracted to John Howard and Co. and the superstructure was built by Associated Bridge Builders.

The design had to deal with certain natural elements. It’s a notoriously windy stretch of water, with the bridge being designed to cope with winds of 100 mph, but it’s also a river that has a fast current and a tidal range of 14.5m in height between low and high tide.

The ‘original bridge’ is actually a series of interconnecting bridges and viaducts forming one complete stretch and one which the motorist is oblivious to they travel between the interchanges. The links are, from England to Wales, the Aust Viaduct, the Severn Bridge, the Beachley Viaduct and the Wye Bridge. The carriageway starts on the English side at the Aust interchange, a road roundabout nearby. As it reaches the end of the land it becomes the 514ft Aust Viaduct, taking it to Aust Pier, a large concrete structure in the river. It then becomes the 5,240ft ‘Severn Bridge’, recognisable by two large tower sections. From Aust Pier the 5,240ft bridge is broken down into 1,000ft of side span to the first tower, the 3,240ft main span between the two towers and the other 1,000ft side span on the Beachley (Welsh) side.

This completes the crossing of the River Severn (at the point where the vertical side cabling ends). The bridge road is now over land, but the River Wye is soon to be crossed, and over the Wye there is a 1,340ft bridge waiting. Between the Severn and Wye bridges there is a 2,023ft stretch of road (the Beachley Viaduct). After the Wye Bridge, the Wye Viaduct takes the road to the Newhouse Interchange. The bridge layout therefore crosses two rivers and ends here.

The two tower sections are made of high tensile steel with each leg being 17ft x 12ft at the base, tapering to 17ft x 9.5ft at the top.

The bridge originally carried the M4 motorway but struggled to cope with the volume, and when the second crossing was opened in 1996, the M4 was diverted to that crossing point with the (original) Severn Bridge road then becoming the M48. Up until the diversion, the bridge had carried 300 million vehicles.

It became clear in the 1970’s with the huge rise in traffic that the method of crossing the Severn would have to be updated at some point as the existing bridge would never cope with the projected volume. An initial study was commissioned by the government with various sections of the community being consulted and in 1989 tenders were invited for two options:

1) To design, build, finance and operate the second crossing which would include operating the first crossing and paying off the debt (DBFO).

2) To design and build the second crossing.

In 1990 the contract was awarded to Laing-GTM, an Anglo-French consortium, with the designers being Halcrow in partnership with French consultants SEEE. It was on the DBFO basis.

The cost was £428m, which was a lot more than the £8m of the original bridge!

The contract details were as follows:

Main estuary crossing and toll plaza – £330m

English approach roads – £65m

Welsh approach road – £24m

British Rail Bridge, Hallen – £1.6m

Rogiet construction access – £0.5m

Enhanced navigation aids – £1.0m

Advanced support structures – £0.6m

Service diversions – £5.6m

Total – £428.3m

The site chosen was 4.8km downstream from the Severn Bridge and runs from Sudbrook on the Welsh side to Redwick on the English side. The crossing is 3.17 miles long (5km) and the bridge carries six lanes of the M4, three in each direction.

The official date for the start of construction was 28th April 1992 and the crossing was opened by the Prince of Wales on 5th June 1996. There were certain design aspects to consider – the aforementioned high winds and tidal range, with much of the tidal problem being alleviated by pre-casting the concrete components on land and transporting them into the river by barge. Another problem was that the bridge had to cross over the Severn Rail Tunnel. In total 10 floating craft were used, with another 7 used as back up barges. The design specification took account of earthquake movement and ship impact and the road is protected by wind reducing fencing.

The foundations of the bridge consist of 37 precast concrete caissons. Each are 53m long and they are laid on the sea bed and it is on these that the vertical concrete piers sit. They were each lifted off the barge and laid in a two hour tidal window. To ensure that each pier had a perfect fit when sitting on the caisson, each individual pier was matched to its individual caisson in the casting yard before being transported and connected under water.

The piers are 107 yards apart, with the central span of the bridge 500 yards long to allow shipping to pass through at the river’s deepest point. The vertical piers vary in height with the tallest being 48m high.

The two sets of pylons either side of the main span are 489ft high and have 240 cables. Secondary cables were subsequently installed as initial cable vibration was greater than expected.

Today the bridge runs smoothly as a perfect continuation of the M4 motorway with the only indication that it’s a bridge, being the toll booths and obviously the marvellous view. One cause for closure happened in both February and December 2009 when falling ice prevented traffic crossing. The bridge can carry over 60,000 vehicles a day. The toll booths phase out in 2018.

 

Severn Bridges Visit

As with most bridges, the easiest way of looking at them is to simply travel across. 

The ‘old’ Severn Bridge is the M48 motorway that travels across the River Severn and then across the River Wye. 

The ‘new’ one is a very long bridge that carries the M4, the motorway that runs through south Wales. Both bridges can be viewed well by simply driving over them.

Nearby cities include Bath, Bristol, Newport and Chepstow.

Tolls end in 2018 after which it will be free to cross in a vehicle.