THE 100 MILLIONTH vehicle crossing of the Humber Bridge was celebrated this week by the original project team.
Sound design, construction and maintenance mean that the bridge's hanger cables are set to exceed their 25 year design life, said bridgemaster Roger Evans, praising the 40 strong reunion.
Evans dismissed speculation that the hangers will need replacing in two to three years time: 'We had budgeted to replace them after 25 years, in 2006, but as we don't have a single defect yet we are confident that it won't be necessary, ' he said.
Evans said that knowledge and experience brought to design of the bridge by consulting engineer Freeman Fox & Partners helped produce a structure of outstandingly high performance.
'Civil engineering moves along in a series of lurches, ' Evans explained, tracing a history of suspension bridge design. 'One of the bigger lurches happened 60 years ago with the Tacoma Narrows Bridge collapse.'
Freeman Fox responded to the tragedy by discarding deep trusses to stiffen the deck in favour of orthotropic steel box structures. This was the method on the Severn Bridge with the deck, like Humber, suspended from inclined hangers. However on the Severn Bridge these had to be replaced in the early 1980s due to faster than anticipated fatigue.
No such problems have yet been identified on the Humber, said Evans: 'We have a bridge brilliant in concept and detail, which means no problems in service. We think inclined hangers are very good.'
Evans commended the serviceability of the bridge, built for £250M at today's prices, but costing just £3M a year to operate and maintain while generating £17M in toll revenue.
Despite this, the bridge will celebrate its 21st birthday this year still almost £350M in debt.
Technical difficulties, labour problems and poor weather all contributed toward the bridge taking nine years to build instead of five, increasing construction costs from £28M to £98M.
By the time the bridge opened to traffic in 1981, debt on the government loans used to finance the scheme had grown to £151M.
'In the early days we were borrowing just to pay the interest on the loans, ' said Evans. 'At the peak we were £450M in debt.'
Finally, in 1998, the scheme was refinanced with lower interest rates and 20% of the debt was written off.
'Now, of the £17M in tolls, £4M pays off the capital and £10M pays the interest, said Evans. 'By 2032 we will finally have paid for the whole bridge.'