Conwy crossings

Year:1826, 1848, 1958 & 1991

Duration:4, 2, 1 & 5 years

Cost:Unknown

Country: River Conwy, Wales

What did this project achieve?

Design and build an even better way for crossing the river Conwy in Wales

In 1826 when the Conwy suspension bridge opened it was one of the first suspension bridges in the world. It replaced a ferry at the same point and is similar to another Thomas Telford suspension bridge over the Menai Strait in Wales.

In 1848 engineers working on the Conwy railway bridge – sometimes called the Conwy tubular bridge – developed a wrought-iron box-girder construction to build the structure. The new method meant the bridge could cross the river in a single span.

The 1958 Conwy road bridge is single arch and made of steel. It carries the former A55 trunk road. Its north side is faced with stone to fit in with nearby Conwy Castle.

The 1991 Conway road tunnel was Britain's first immersed tube tunnel. This is a tunnel where segments of the structure are prefabricated then floated into place and joined together.

Difference the crossings have made

In 1826 the Conway suspension bridge was the first crossing over the Conwy river. Replacing an unreliable ferry service, it made movement of goods and people in the region easier and boosted the local economy.

Around 20 years later the Conwy railway bridge carried the Chester to Holyhead line over the river. The bridge helped cut journey times between the two towns.

The 1958 Conwy road bridge was designed to ease pressure on the 1826 suspension bridge. After the road bridge opened it was closed to all but pedestrian traffic.

The 1991 Conwy tunnel reduced traffic on the 1958 road bridge and cut road congestion and air pollution in the area.

How the work was done

Engineer Thomas Telford designed his suspension bridge to match the nearby Conwy Castle. The towers on each end were castellated – made to look like battlements.

Engineers anchored the suspension chains on one end of the bridge to a concrete plinth on the east side of the river. Chains on the other side were anchored to the barbican (outer wall) of the castle.

Engineer Robert Stephenson's Conwy railway bridge was the first – and only surviving – tubular bridge in Britain. He delayed its opening so he could run tests to confirm the structure would carry the weight of engines and rolling stock.

Engineers working on the 1958 95m-long road bridge used rounded support columns at each end to reflect the look of Conwy Castle.

The 1991 Conway tunnel was constructed from prefabricated segments. Engineers floated the segments into the estuary as the tide rose and sank them into the river as the tide fell.

The units rested on concrete pads. They were then joined together underwater.

"​‌

It was like walking through six submarines end to end. It was a quite amazing engineering feat - the first immersed tube tunnel in the UK.

Lord Wyn Roberts

Former Welsh Office minister, who commissioned the road tunnel, remembers walking through it when nearly-finished, talking to local newspaper the Daily Post in 2013

Fascinating facts

The Conwy railway bridge still carries intercity and regional train services along the north Wales coast line.

Soil and earth dug out from the Conwy tunnel were used to build a bird sanctuary on the east bank of the river: the Glan Conwy Nature Reserve.

The Conwy tunnel casting basins – flooded areas used during construction work – also found another use. They were converted into what is now the 500-berth Conwy marina.

People who made it happen

  • Conwy suspension bridge designed by Thomas Telford, first ICE president
  • Conwy railway bridge designed by Robert Stephenson, ICE president
  • Conwy road bridge constructed by engineers Sir William Arrol & Co
  • Conwy tunnel designed by engineers Travers Morgan, now Capita Symonds

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