On 14th and 15th July 2020, the Clifton Suspension Bridge closed to traffic from 9.30am to 3.30pm. But why was this necessary, and what took place during the six hour window each day?
In engineering terms, every car or person crossing the Clifton Suspension Bridge is a ‘dynamic load’ – a weight which moves across the bridge causing a small amount of wear and tear. As thousands of people and cars cross the bridge each day, the wear and tear to the structure can soon add up! Most bridges are inspected thoroughly every six years, but as the Clifton Suspension Bridge is a Grade I listed structure with over 90% of its original ironwork still in place, the Clifton Suspension Bridge Trust ensures the bridge is completely inspected every three years. This work is spread out over the years and each year a third of the inspection tasks are carried out to ensure that the bridge remains in tip-top condition. Checks are completely funded by the tolls paid by drivers throughout the year.
In 2020, contractors from our specialist companies were on-site, alongside the Trust’s own engineers and maintenance team to carry out maintenance and inspection. As you can imagine, the coronavirus restrictions meant that even more careful planning than usual was required in order to ensure that each team was able to maintain social distancing!
The main focus of the 2020 closure was the inspection of the vertical shafts which provide access to the back of the anchorages – the location more than 20 metres underground where the suspension chains are fastened to the bedrock. Our fearless engineer had four of these to inspect in one day and with no ladder in place, the only means of access is to be harnessed to a winch and wound down! The engineers also inspected the carriageway and footways for signs of wear and tear.
We also wanted to inspect the Leigh Woods buttress under the tower and to do so we trialled a drone to carry out the survey for us, as it is not an easy area to access and normally requires engineers to abseil down, or the installation of a large amount of scaffolding. Drones are not usually allowed to fly so close to the bridge, so this is something that is only possible by a specialist team during a traffic closure.
One area that was showing signs of wear was the white lining across the bridge, by the toll plazas and on the cycle lanes. The white lines are especially important to cyclists as they signpost a safe route around the toll barriers. We took the opportunity to get these refreshed and our lining contractor worked hard and finished the whole bridge in a day! At the same time, our toll barrier contractor carried out a service on the toll barriers. They are more complicated than you might think and a lot of technology is encased within the barriers in order to raise them for contactless payment, register bridge crossing cards and tell users when their balance is running low.
Out on the bridge itself, we had our specialist electricians replacing some of the LED lights on the buttresses and a few more on the bridge chains. Although there are still a few lights out on the higher parts of the chains (which will require roped access to repair at some point in the future), the majority of the lights are shining brightly again! We have a number of cameras on the bridge that monitor traffic and pedestrians as well as the bridge itself. Our CCTV contractor was there on both days to upgrade some of the cameras and to clean and service the others. You might have seen them in the cherry picker if you were crossing. We also used the cherry picker to replace our contactless only signs to make them clearer for our road users.
Finally, the annual closure also allowed us to catch up on some of our regular maintenance which can only be carried out easily without traffic. The Clifton side weigh beam (which checks the weight of vehicles approaching the bridge and sends an alarm to the toll house if an overweight vehicle approaches the bridge) was lifted out, cleaned and serviced. Weighbridges are extremely important as vehicles weighing more than 4 tonnes have the potential to cause damage to the bridge if they are allowed to cross.
And one last very important job took place to help drivers entering Leigh Woods – North Somerset Council also used the closure to replace a keep left sign on the island by the bridge which will help drivers to see the raised edges of the kerb more easily.
All in all, our 2020 annual closure was a very effective and productive two days work. We’d like to thank all the drivers who crossed the bridge this year for contributing towards the cost of this important maintenance project and thank you to you all for your patience during the closures.