A tunnel replacement for Hammersmith flyover in west London could be built in just three years and release around £1bn worth of former highway land to help pay for the works.
That is the conclusion of a Halcrow-produced feasibility study commissioned by Hammersmith & Fulham Council.
The findings were presented to the council’s transport committee this week.
Halcrow, part of CH2M Hill, has been working with the council on a plan to replace the flyover with a tunnel since the key route was closed for emergency repairs in 2011.
It has now come up with three tunnel options which the council is urging Transport for London (TfL) to assess in more detail.
The alternatives vary from 1.6km to 4.1km in length and are likely to cost between £218M and £1.3bn.
The cheapest option would be a short cut and cover tunnel.
The other, longer options would be twin bored tunnels. These would be marginally quicker to build but far less traffic would use them, Halcrow believes.
As little as 50% of traffic currently using the flyover would use the longest bored tunnel, it has calculated, as there would be fewer entry and exit points.
Halcrow believes all options are geotechnically feasible, running up to 25m deep in the thick band of London clay beneath Hammersmith.
The report also estimates that around £1bn could be recouped from developers building on the land freed up by demolishing the flyover. This is a key factor. TfL commissioner Peter Hendy said in October that there may be an economic case for tunnelling if the value of land released for development on the surface was significant enough (NCE 23 October).
“Why wouldn’t you contemplate that option?” he asked. “Having our minds open to something like that is important.”
Hammersmith & Fulham Council leader Nicholas Botterill said: “This detailed report spells out three possible ways to replace Hammersmith flyover with a flyunder,” said council leader Nicholas Botterill.
“From a shorter tunnel that would act as a catalyst to transform our divided town centre to something longer stretching into neighbouring boroughs, we now know there are at least three ways to tear down Hammersmith’s Berlin Wall.
“Each of the options has pros and cons, but we are now clear that they are possible and, in one case, may even be self-financing - which is an important factor for taxpayers,” he said.
The study, which will include feedback from the House of Commons transport select committee, is set to be finalised by March when it will be presented to TfL, which owns and manages the flyover.
Botterill urged TfL to take the report seriously.“The council has been true to its word and started the process of pulling together the initial details that could enable this major infrastructure project to become a reality, he said.
“But this is only the beginning. There is still much work to be done and it is now up to TfL to use our report as a foundation and take the project through to the next stages of development.”
Meanwhile, TfL is continuing phase two of its work to strengthen the flyover. This will extend the life of the 53 year old structure by another 100 years.