On Dec 2, 3:39*pm, Tom Anderson wrote:
My gut feeling is that adding a third bore to a two-bore setup is a lot
more expensive than adding a footbridge to a railway bridge. In fact, i
can't see how there being two bores there already makes the third any
cheaper, so it would be as expensive as building it as a standalone.

The DLR Woolwich Arsenal twin tunnels were built by sending one boring
machine from King George V to Woolwich, turning it round, and sending
it back again. So in theory you could give it another twirl (probably
works OK time-wise too, as fitting out a rail tunnel takes a lot
longer than fitting out a foot/cycle tunnel) for at least *some* cost
savings.

--
John Band
john at johnband dot org
www.johnband.org