AECOM’s task requires a range of technical skills including transport planning, highway engineering and environmental studies and is expected to take 12 months to complete.
The Dartford River Crossing was first opened in 1963, a second tunnel followed in 1980 and the Queen Elizabeth Bridge became operational in 1991. The objective of this study is to help develop the longer-term strategy for the crossing. The study will consider options to provide additional river crossing capacity in the lower Thames area. It is intended the study will help inform public consultation on options during 2013.
The Lower Thames Crossing was proposed in 1989 in the Roads to Prosperity paper but this was then cancelled in the early 1990s. Three main options have been proposed in the past, all with locations to the east of the existing Queen Elizabeth Bridge. Two of these options would connect from an existing dual carriageway close to Tilbury on the north of the Thames and then take different routes to link with the A2/M2 to the south. One of these last options would also connect with the M20.
There are a range of factors to consider, including the fact that the routes would have to negotiate protected areas. The Lower Thames Crossing would also have to be designed so as not to impede flights to and from City Airport. One of the earlier designs proposed the use of a concrete box girder bridge, which would feature a low profile and therefore not impede on the flightpath for the airport. But the span required would have been at the limit of the technology available at the time using the concrete box girder bridge structure and there were concerns over its structural strength. There were also criticisms that this comparatively cheap construction method would result an extremely ugly design. The design and construction techniques surrounding concrete box girder bridges have improved since the early 1990s and it seems feasible that such a structure might now be feasible. But it might still attract negative comment over its appearance and with approvals being a necessary part of its eventual construction, could well prove yet another barrier to the project.
While cable stayed bridges are favoured on grounds of aesthetics and also offer manageable costs if built along conventional lines, such a structure could intrude on the safety parameters for the flightpath into the airport. Another proposal has been to include the crossing as part of the proposed Thames Barrier but this may face further obstacles on various environmental grounds as well as cost issues. Balancing all the factors for the project will be a complex task and AECOM is likely to put forward various options. At this stage however it seems likely that the concrete box girder option, however ugly, will be cheapest and simplest and with costs of any transport connection under the spotlight due to tough budgetary constraints, it will have a very strong case in its favour.