LONDON'S TOWER Bridge could be severely weakened if extra traffic is forced over it as a result of the introduction of congestion charging in the capital, its owner City of London Corporation said this week.
Urgent talks are taking place between the Corporation and congestion charging promoter Transport for London (TfL) in a bid to head off a rapid acceleration of structural damage after charging takes effect in 2003.
The 105 year old double bascule bridge will be just outside the eastern edge of the planned charging zone.
As a result, motorists wanting to avoid the £5 congestion charge are expected to cross the Thames using Tower Bridge instead of river crossings inside the charging zone immediately to the west.
'There is a fear of more HGVs diverting to the bridge if they bring in the scheme, ' said the Corporation's strategic transport director Joe Weiss.
'And the bridge can't take too many 38t continental tour buses diverting on to it. There is a danger of overstressing various structural members, accelerating decay to parts of it.'
Concern centres on the mid point of the bridge where the two bascules meet.
An estimated 38,000 vehicles use the bridge each day, pushing it to capacity during peak hours.
The Corporation of London's bridge consultant High Point Rendel is already working on a rehabilitation programme for the bridge amid fears that failure to enforce the 17t weight limit and 20mph speed limit has led to considerable weakening of the structure.
Extra traffic is expected to increase impact damage to the extremities, which flex under traffic loads.
Options for preventing an acceleration in structural damage include restricting access on approaches to the bridge with width restrictions and traffic islands.
Traffic management solutions under discussion with TfL and consultant Oscar Faber include 'tuning down' traffic signals, by increasing the frequency of red lights on the bridge approaches, to slow traffic flows so that vehicles reach the bridge less quickly.
Taken as a whole, the measures could cost TfL up to £30M.
But these measures are expected to increase congestion either side of the bridge, adding to delays caused when it opens for shipping. Last year Tower Bridge lifted 925 times.
The Corporation of London has suggested further study into the diversion of traffic to the bridge but TfL has not agreed.
TfL director of street management Derek Turner told NCE this week: 'We do appreciate that there is a lack of enforcement of the current weight limit on the bridge at the moment and we are working with the Corporation of London to improve that.'
But he added: 'The diversion effects to Tower Bridge will be pretty low. I do not think there is a need to move the inner ring road as the boundary of the scheme.'
However, the Corporation of London is so worried about the Grade One listed structure that it is lobbying for the eastern boundary of the congestion charging zone to be moved to the twin bore Blackwall Tunnel.
The tunnel's capacity matches that of Vauxhall Bridge, which is just outside the western edge of the charging zone.
'Surely the capacity of the eastern perimeter river crossing should be the same as that in the west, ' said Weiss.
Meanwhile, business lobby group London First is pushing for a free route through the middle of London starting at Blackfriars Bridge. This could ease pressure on Tower Bridge and other congestion pinch points likely to be created by the congestion charging scheme.
Turner rejected this idea. 'We do not want to encourage through traffic in central London at all, ' he said.
TfL is expected to publish more details of how it will preserve Tower Bridge in its transport strategy to be published next month. Congestion charging is expected to be confirmed in the strategy after TfL claimed that 51% of those surveyed were in favour of the scheme.