Second Severn Crossing

From Wikipedia, the free encyclopedia

Second Severn Crossing
Second Severn crossing seen from the English side looking West, January 2006
Carries	6 lane M4 motorway
Crosses	River Severn
Locale	South West England/South East Wales
Design	central span: Cable-stayed bridge approach viaducts: Segmental bridge
Longest span	456 metres
Total length	3.186 miles (5.128 km)
Opening date	5 June 1996

The Second Severn crossing, seen here from the English side of the river, carries the M4 motorway between England and Wales. The shipping channel lies between the two towers

The Second Severn Crossing is a motorway crossing over the River Severn between England and Wales, inaugurated on 5 June 1996 to augment the traffic capacity of the original Severn Bridge crossing built in 1966. The bridge marks the lower limit of the River Severn and the start of the Severn estuary.

Its location is further to the south than the old bridge and being more in line with the landward sides of the M4 motorway, is a shorter journey when travelling from England to South Wales. The junctions at each end are designed for most traffic to use this crossing – to use the old Severn Bridge crossing one has to leave the M4 and join the M48 motorway either at Aust or near Magor. The new crossing carries more traffic than the Severn Bridge which continues in use. It is wider than the Severn Bridge, having three lanes and hard shoulder each way, compared to the 2 lanes and cyclepath/footpath of the original crossing.

The crossing is 3.186 miles (5.128 km) long, consisting of a single central navigation span over the "Shoots" channel and approach viaducts on either side. The Shoots channel is the deepest section along the width of the Severn estuary and a longer span was required to ease the passage of shipping under this section. The central bridge section, called the Shoots Bridge, is of cable-stayed design and the central span (between the bridge pylons) is 456 metres in length. The approach viaducts are of a segmental bridge design. Its Welsh end is in Monmouthshire; its English end at Severn Beach in South Gloucestershire. The crossing forms a gentle S shape and near the English side crosses over the top of the Severn railway tunnel.

The sides of the bridge are fitted with special railings to reduce lateral wind loads coming from the Severn estuary onto the traffic and 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.

[edit] Tolls

In contrast to the original Severn Bridge crossing, the tolls are collected on the Welsh side near Rogiet (but in the same direction as on the first crossing). Tolls can be only be paid for by cash, cheque, or by use of the Severn TAG system. The Severn TAG is a wireless system where payments are paid electronically as vehicles drive through the toll lane.

Tolls charges are based on a three tier pricing system:

Motorcycles and other vehicles driven by a UK disabled badge holder are exempted from paying a toll, although these vehicles must stop at the toll booth to confirm their eligibility.

The toll prices are updated every year on January 1st in accordance with the Severn Bridges Act of 1992.

[edit] Construction

The crossing was built by a business consortium under a Public-private partnership. A company called Severn River Crossing Plc was formed to build the new crossing. The 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 expected to be paid for by tolls collected from motorists using the two crossings. Work on the new crossing began in 1992 with completion in 1996.

Prior to construction, there was controversy over the environmental impact to the surrounding area. The approach viaducts on the east side are built on the English Stones, a rocky outcrop which is uncovered at low tide. The crossing is built near extensive mudflats in the Severn Estuary, which are used by migrating birds. The main concerns were the immediate damage that could arise from construction work and the longer term problems of traffic pollution.

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, prior to being floated-out on the high tide to the appropriate site. Each bridge pier foundation consists of a concrete pneumatic caisson which is sunk into the mud of the estuary. The decking on the approach viaducts consist of 3.5m match cast sections which are post stressed.

The cable stayed section of the crossing is over 900m long, consisting of a 35m wide deck made from steel plate girders with a composite reinforced concrete slab. These were prefabricated on shore and put in place using balanced cantilever methods. There are two 149m high twin leg, reinforced and pre-stressed concrete pylons carrying 240 cables which support the bridge deck. Cable vibrations were experienced during construction and secondary cables were added to eliminate this. To avoid detracting from the aesthetics of the primary cables, the secondary cables are very slender and are not very noticeable.

[edit] External links

• Severn River Crossing PLC
• The Motorway Archive: M4 Second Severn Crossing
• Timelapse video of the crossing on Youtube

• Maps and aerial photos Coordinates: 51.57589° -2.70692°
  • Satellite image from WikiMapia or Google Map
  • Street map from Multimap or GlobalGuide
  • Aerial image from TerraServer

• River Severn Bridges