Tamar Bridge
The Tamar Bridge, adjacent to the more famous Royal Albert Bridge, is a major road bridge at Saltash carrying traffic between Cornwall and Devon over the River Tamar. When it opened in 1961 it was the longest suspension bridge in the United Kingdom. In 2001 it became the world's first suspension bridge to be widened (from three to five lanes) using cantilevers. The five lanes are divided as follows: three lanes carry the A38 trunk road (the middle lane being a reversible lane), the fourth is reserved for eastbound local traffic and the fifth for pedestrians and cyclists. Previously all traffic merged and shared the three lanes.
Construction of the Tamar Bridge began in July 1959. Before this, the lowest road crossing of the River Tamar was Gunnislake New Bridge at the village of Gunnislake. This seven-arched granite bridge was built in the early 16th century (c. 1520). It is still in use today but it is only wide enough to carry one lane of traffic. Before the Tamar Bridge was opened, most car drivers wishing to travel between Saltash (on the Cornish side) and the Devon city of Plymouth used car ferries. Today the Tamar Bridge carries approximately 40,000 vehicles every day. It is co-owned by Plymouth City Council and Cornwall Council, and is managed by the Tamar Bridge and Torpoint Ferry Joint Committee. A toll of £1.50 per car is charged when driving from Cornwall into Devon, although the price is halved using the electronic payment system. Motorcycles do not have to pay.
The Tamar Bridge is located above the Hamoaze, and runs parallel to Isambard Kingdom Brunel's Royal Albert Bridge which opened in 1859 and is considered to be one of his greatest railway achievements. Both bridges offer wonderful views of the Tamar Valley and Tamar Estuary. The Tamar, Lynher and Tavy Valleys form an Area of Outstanding Natural Beauty.
Construction of the Tamar Bridge
Why it was needed
In the 1950s (and for centuries before this) road users wishing to drive from Saltash to Plymouth had two main choices: They could take a long detour north either to Gunnislake New Bridge (a one-lane mediæval bridge) or even further north to the land-link between Devon and Cornwall, or they could cross the river by ferry. For centuries there was a ferry link between the two counties just downstream from the current bridge, but the ferries did not have sufficient capacity to transport large numbers of vehicles as traffic volumes increased. After failing to secure government funding for a new road bridge, Plymouth and Cornwall councils applied for permission to operate a toll bridge for which they received Royal Assent in 1957.
Construction
The Tamar Bridge was the first major suspension bridge to be constructed in the UK after the Second World War. It was also the longest suspension bridge in the UK at that time. Its central span measures 1,100 ft. The bridge was constructed by Cleveland Bridge and Engineering Company, and building work began in July 1959. It had a concrete deck, and was capable of carrying lorries up to 38 tons. The construction cost over £1.5 million, and the bridge opened to traffic in October 1961. H.M. Queen Elizabeth, The Queen Mother officially opened the bridge on 26 April 1962.
Tamar Bridge in use
The bridge was three lanes wide (until 2001, see below). Local traffic had to merge with traffic from the A38 trunk road, which runs from Bodmin in Cornwall to Mansfield in Nottinghamshire (approximately 300 miles). The point at which the two streams of traffic merged to cross the bridge into Devon was a notorious accident black spot.
In 1961, approximately 4,000 vehicles used the Tamar Bridge each day. This had dramatically increased by the 1990s. In 1998 the hourly rate during the morning rush hour was 2,500 vehicles. The average weekday saw 38,200 vehicles cross the bridge and the summer weekday flow was even higher at 42,900 (the Tamar Bridge is an important tourist route into Cornwall). In contrast, the Torpoint ferry link could transport a maximum of 300 vehicles per hour.[1] The Torpoint Ferries operate between the Cornish town of Torpoint and the Devon city of Plymouth; this is more southerly crossing than the Tamar Bridge, linking Torpoint and the Rame Peninsula to Devon. As such it is not in competition with the Tamar Bridge, in fact the Tamar Bridge and Torpoint Ferry Joint Committee manage the bridge, and revenue from its tolls subsidise the Torpoint ferries.
Widening and strengthening
Motivation
In the late 1990s, after nearly four decades of use, it was found that the Tamar Bridge would not be able to meet a new European Union directive that bridges should be capable of carrying lorries up to 40 tons. In fact, the concrete deck had deteriorated so much that the weight limit for vehicles crossing bridge was in danger of being reduced to 17 tons. It was agreed that this restriction would damage the local economy, so the bridge needed to be strengthened or replaced.
It was estimated that building an alternative river crossing would cost in excess of £300 million. Once a viable strengthening scheme was proposed, the idea of building a new bridge was abandoned due to the high cost. The main problem with strengthening the Tamar Bridge was that since it catered for around 40,000 vehicles a day, closing it for the duration was not a viable option. An engineer proposed temporarily adding cantilever platforms to the sides of the bridge to accommodate traffic while the main deck was strengthened. Once this revolutionary technique had been accepted, it was soon decided that these two extra lanes should be permanent additions to the bridge to increase the number of lanes from three to five.
This additional capacity was not expected to encourage a large increase in the number of vehicles using the Tamar Bridge. The A38 road passes through the three-lane Saltash Tunnel on the Cornish side of the bridge (this acts as a subterranean bypass for Saltash and opened in 1988). The tunnel was expected to regulate the amount of traffic using the bridge despite the increased capacity. The real benefit of these extra lanes would be to make the Tamar Bridge safer and more pleasant for all types of traffic. Pedestrians and cyclists would be safer since they were properly separated from all motor vehicles. Also, local traffic eastbound from Saltash would no longer have to merge with the A38, eliminating a notorious accident black spot.
Progress
The principal designer of the strengthening and widening of the Tamar Bridge was Hyder Consulting Ltd, and the principal contractor was Cleveland Bridge UK Ltd (who originally built the bridge). The overall cost was approximately £34 million (a fraction of the estimated £300 million for a new bridge). This was funded from the revenue from tolls paid to cross the Tamar Bridge into Devon.
Work began on the Tamar Bridge in March 1999 and was completed, one month behind schedule, in December 2001. At one point the project was three months behind schedule. The delays were due both to an embargo on road works for the total solar eclipse of 11 August 1999 which saw tourists flock to Cornwall, one of the few areas of the UK in the path of totality, and also due to extremely bad weather during the winter of 1999/2000. The improved bridge was fully opened to traffic on 20 December 2001 (although it was never fully closed, in fact during peak hours every effort was made to keep three lanes open). The Tamar Bridge was officially reopened by Princess Anne on 26 April 2002-forty years to the day after it was first officially opened.
Construction methods
The Tamar Bridge originally had a concrete deck. This had degraded so seriously over its four decades of use that rather than simply being reinforced it was entirely replaced by an orthotropic steel deck (i.e. a deck formed from steel plates supported underneath by longitudinal ribs or stiffeners). The members were also strengthened by the addition of steelwork, and 18 new diagonal cable stays were fitted. The two new cantilever lanes were added to the bridge before the old concrete deck was replaced so as to be available to diverted traffic. At all times during the project, the importance of maintaining the flow of traffic over the bridge was emphasised. Even during construction work the Tamar Bridge served approximately 40,000 vehicles a week.
When modifying suspension bridges engineers have to be constantly aware of the distribution of weight. At first, steel may sound like an unlikely choice of construction material for the replacement deck, especially since the bridge will have to support five lanes of steel deck instead of the original three of concrete. However, even with the replacement steel deck and the addition of two cantilever lanes, the new bridge weighs only 25 tons more than the original.
The new steel deck is formed from 82 orthotropic panels. Each panel weighs 20 tons, and measures roughly 50 ft by 20 ft. They were constructed in Darlington, County Durham by Cleveland Bridge UK Ltd and driven nearly 400 miles to the Tamar Bridge and welded together on site.
Recognition
The Tamar Bridge is the world's first suspension bridge to be widened using cantilevers, and the world's first suspension bridge to be widened and strengthened while remaining open to traffic. The strengthening and widening project was:
- the winner of the highly prestigious British Construction Industry Civil Engineering Award for 2002[2]
- the winner of the Historic Structures category (30 years or older) of the Institution of Civil Engineers Awards 2002[3]
- one of eight finalists for the Prime Minister's Better Public Building Award 2002[4]
Signage
On 8 February 2008, two bi-lingual signs were put in place of the original sign welcoming visitors into Cornwall. They are situated on both pillars of the west bank on the Cornish side. They read "Welcome to Cornwall", "Kernow a'gas Dynergh". On the east bank the signs are in English and read "Welcome to Plymouth".
References
Outside links
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("Wikimedia Commons" has material about Tamar Bridge) |
- Plymouth City Council
- Cornwall County Council
- Official Tamar Bridge website
- Official Torpoint Ferry website
- From the Select Committee on the Tamar Bridge Bill (widening and strengthening)
- Hyder Consulting Ltd
- Cleveland Bridge Ltd
- The British Construction Industry Awards
- Institution of Civil Engineers
- Better Public Building Awards