THE familiar “bump-bumps” as vehicles drive across the Forth Road Bridge will become a thing of the past under a new scheme to upgrade the carriageway.
Work will start later this year on a trial replacement of the joints linking the 18-metre lengths of roadway which make up the bridge.
Motorists are being warned the £440,000 project will mean massive disruption with weekend carriageway closures being planned for September.
But if the trial is a success, it could pave the way for all but eliminating the familiar bumps and giving drivers and their passengers a more comfortable journey.
Bridgemaster Barry Colford said in the 48 years since the bridge was opened there had always been some sensation from driving over the joints, but the “step” between the sections or roadway was now 20mm in some cases and growing.
He said: “The scheme, if successful, would not eliminate the joints. There would still be a feeling as you passed over them, but the aim is to reduce the impact of these ‘steps’.
“Our regular users are fairly used to it, but it would make the ride quality for users a lot more comfortable.
“A 20mm step doesn’t sound a lot, but you can feel it and it resounds through the structure as well.”
He said “re-levelling” the joints was “one of our biggest maintenance problems”.
“We spend a lot of time using overnight carriageway closures trying to do repairs, but the temporary fix only lasts for between six and 12 months and then we have to do it again, he said.”
A new design of joint could provide a longer-term solution.
He added: “Comfort is not the main reason we are doing it – we are trying to offset some of the effects on the bridge – but if we can make the journey smoother for our users, who are the most important people, that’s a great benefit.”
The weekend closures are expected to mean north and south-bound traffic sharing one side of the bridge in a contra-flow arrangement.
When similar measures were used last October, it led to three-hour queues in both directions.
Bridge officials said today they were still looking at how the work could be carried out in a way that kept closures to a minimum.
But they admitted it would mean “a great deal of inconvenience” for bridge users.
There are 768 such joints in the bridge, but only a limited number will be replaced in the trial scheme.
In report to the Forth Estuary Transport Authority, which operates the bridge, Mr Colford identified a money-saving design as the root of the problem.
He wrote: “The joint detail appears to have been chosen at the original design stage to reduce the size and cost of the supporting girders and this would have also led to savings elsewhere in the bridge design, most notably in the main cables.
“Unfortunately, this design saving has led to significant maintenance costs over the last 20 to 30 years.
“From the users’ point of view the increasing step does cause issues with ride quality and there have been a lot of adverse comments.”
Most of the work is expected to be carried out using overnight carriageway closures, but Mr Colford said some work on strengthening and welding of existing steelwork may need longer closures.
September had been identified as the most suitable month for weekend closures, taking into account factors such as weather and inconvenience to bridge users.
A spokesman said: “We are hoping to minimise the closures and the disruption, but it is likely we will need to have some degree of closure on more than one weekend.”