Still not very rigorous!Peter Freeman wrote: ↑Fri Nov 04, 2022 12:53My estimate that the option A14 total cost would be lower than the current plan was my own amateur estimate, based on the simplicity of the task: one twin tunnel, two TBMs, two over-bridges for the forks, and a bit of M25 widening here and there. TBMs are expensive, but not all that expensive. Immersed tube segments are also expensive, and tricky to handle. The technology and usage of TBMs seems to be quickly advancing. However, I accede to your more rigorous estimating.jackal wrote: ↑Thu Nov 03, 2022 15:27The bored tunnel for this option appears to be some 7.5 miles, three times longer than the proposal. ...Peter Freeman wrote: ↑Thu Nov 03, 2022 13:44 ... Despite the longer tunnels, using TBMs, it would turn out to be lower in both cost and all adverse impacts. ...
... This is 23% more than the £5.3bn contract cost for the LTC as developed.
I was also influenced by hearing a rumour, mid-this-year, that the Sydney Western Harbour Tunnel, planned so far to be immersed tube, was considering a switch to TBM. Today, that rumour was confirmed -
https://www.smh.com.au/national/nsw/maj ... 5bv0g.html
Just to clarify, the LTC tunnels will also be bored. Immersed tube and bridge alternatives were considered but rejected. The price for the immersed tubes was pretty much the same as the bores while having more environmental impact. Either way you are looking at 5-10 times the cost of a surface route.