Trifter

River bridges along the motorway.

Sometimes we think of motorways as dull affairs, merely a means of getting from A to B.  We overlook the engineering achievements that are required to develop and maintain a national road network.  There are many estuaries and river crossings where a technically challenging solutions have clipped miles off of the original route.

Here, I have sampled just some of these achievements in England and Wales. 

English Bridges

The Avonmouth Bridge (M5)

The Avonmouth Bridge carries the M5 motorway across the River Avon near Bristol.  It is a hollow box cantilever construction.  The main span is 538 ft (164 m) long, and the bridge is 4,554 ft (1,388 m) long.  The bridge carries an eight lane highway and a bridleway for foot passengers, bicycles and mopeds.  The bridge climbs steeply to accommodate tall ships.  The steep gradient causes heavy vehicles to slow down leading to heavy delays during rush hour and the summer tourist season.

The Dartford Crossing/Queen Elizabeth II Bridge (A222/M25)

The Dartford Crossing/Queen Elizabeth Bridge is the lowest crossing on the River Thames.  Construction began in August 1988 as part of a Private Finance Initiative (PFI) project and was completed on 7 June 1991. The bridge takes southbound traffic across the Dartfon Crossing.  The two older tunnels carry northbound traffic.  Until the completion of the Second Severn Crossing in 1996 (which is 6m longer) this was the largest cable-stayed bridge in the United Kingdom.  It is 137 m (449 ft) metre high and 812 m (2,664 ft) metres long.  The deck is supported by cables attached to 84 m (276 ft) metre high steel pylons that rise above the road deck.  At the highest point the road deck rises 65 m (213 ft) above the river.  This gives 57.5 m (189 ft) clearance to shipping.

The Humber Bridge (A15)

The Humber Bridge spans the Humber near Kingston upon Hull.  This is the firth largest single-span suspension bridge in the world.  Construction began on 26 July 1972 and was completed on  17 July 1981.  Freeman Fox & Partners were consulting engineers for the project.  The bridge carries a dual carriageway with a lower-level foot and cyclepath on both sides.  It  has a centre span of 1,410 metres (4,626 ft) and a total length of 2,220 metres (7,283 ft).  Each tower is 155.5 metres (510 ft) tall.  The north tower is on the bank with foundations that go down to 8 metres (26 ft).  Foundations for the south tower which is in the estuary descend 36 metres (118 ft) to avoid the shifting sands that make up the estuary.  The suspension cables contain nearly enough wire to circle the Earth twice.  The bridge carries an average of 120,000 vehicles per week.

The Thelwall Viaduct

The Thelwall Viaduct carries the M6 motorway across the Manchester Ship Canal and the River Mersey.  The viaduct includes two entirely separate bridges: one carries the northbound carriageway (opened in July 1963), the other the southbound carriageway (opened in 1995).  Both are approximately 1.35 km long.  The longest span is 102.4 m over the Ship Canal.

The Severn Bridge (M48)

The Severn Bridge carries the M48 motorway across the River Severn.  The suspension bridge took five years to construct.  It was opened on 8 September 1966.  The crossing includes four structures: the Aust Viaduct, Severn Bridge, Beachley Viaduct and Wye Bridge.  The suspension bridge took five years to construct and was opened on 8 September 1966.  It is 5,240 ft (1,600 m) long. It has a 3,240 ft (988 m) central span and the two 1,000 ft (305 m) side spans.  The towers rise to 445 ft (136 m) above mean high water.  The shape of the bridge was determined by the designers Freeman, Fox and Partners following wind tunnel tests for the Forth Road Bridge.  In the late 1980s the crossing was strengthened and resurfaced.  The difficulty of organising continued maintenance while faced with heavy traffic volumes led to the construction of the Second Severn Crossing.  At its peak, the Severn Bridge carried 50,000 vehicles a day.  It currently carries about 15,000 vehicles day, or 25% of the total traffic traversing the estuary.

The Second Severn Crossing (M4)

 The Second Severn Crossing carries the M4 motorway over the River Severn.  It  was constructed to augment the traffic capacity of the original Severn Bridge.  The crossing is further south than the original bridge and demarks the point where the River Severn becomes the Severn Estuary.  Building at this site reduced the motorway mileage between London and South Wales but required a longer crossing.  The crossing was constructed by the Severn River Crossing Plc under a public-private partnership. Work began in 1992 and was completed in 1996. 

The crossing is 3.186 miles (5.127 km) miles long.  The approach viaducts form a gentle S shape.  The cable-stayed bridge that traverses the deep water “Shoots” channel was designed to ensure that the channel remained open to shipping.  The central span (between the bridge pylons) is 456 m (1,500 ft) in length.  The 37 bridge pier foundations on the approach viaducts are 98.11 metres (321.9 ft) apart.  The cable stayed section is over 900 metres (2,953 ft) long.  Two 149 metres (489 ft) high twin leg, reinforced and pre-stressed concrete pylons carrying 240 cables which support the bridge deck.  The bridge is equipped with special railings to reduce lateral wind loads.

Welsh Bridges and River Crossings 

The Britton Ferry Bridge (M4)

This bridge carries the M4 across the River Neath to the south of the town of Neath. When completed in 1994, it completed the M4 project.  Long reinforced concrete approach viaducts converge from each side of the Neath Estuary towards an imposing steel viaduct bridge that crosses the river. The deck is supported by eight rows of steel plate girders, These girders, weigh almost 4000 tonnes in total.

The Usk Crossing (M4)

This crossing carries the M4 motorway across the River Usk near Newport.  Two separate 450 ft (140 m) bridges carry east and westbound traffic.  When travelling westwards, the bridges lead directly into the twin 1,200 ft-long Brynglas Tunnels. These were the first tunnels in the British motorway network and are still the only bored tunnels.  Work commenced on the bridge and the tunnels in September 1962 and was completed in May 1967.

If you enjoyed this article you might like to visit my other articles on bridges

Spectacular Transportation Bridges