🚀 go-pugleaf

Colin R. Leech wrote:
> 
> "Scott M. Kozel" (kozelsm@richmond.infi.net) wrote:
> >
> > Expressways can be undergrounded for about the same per-mile cost as a
> > subway.
> 
> Per lane-mile, perhaps. But it's most certainly going to cost a lot more
> per mile to bury a 10 lane highway than a two track rail line.
> 
> > The Big Dig is an exception, so don't mention it.
> 
> The realities that don't agree with your preconceived notions always seem
> to be "exceptions".
> 

The realities vary a bit.

The I-95 (currently I-395) highway tunnel in Washington, D.C. was built
upon a straight line in a relatively open area.

The Boston Central Artery Tunnel Project (the burying of downtown Boston
I-93,and the extension of the I-90 Boston Turnpike) are more complex
projects, involving a curving alignment through a built up area largely
beneath an existing elevated expressway that is being maintained during
the construction duration (for the downtown I-93 segment), and an
entirely new underground extension through soil that has been described
as being similar to jello (for portions of the I-90 segment linking the
existing Tunpike to the new Ted Williams Tunnel).  Furthermore, because
of the nature of the existing city infrastructure, Boston's CA/T
project  includes the replacing/relocating of much other buried
infrastructure, such as utility lines that criss-cross beneath the
existing elevated highway, along with maintaining nearby historic
buildings, the foundations of which were never designed for handeling
the excavations of the CA/T project, and thus must be shored up.  This
stands in contrast to the conditions surrounding the I-95 Mall Tunnel
and even the unbuilt I-66 K-Street tunnel, which would be a constructed
upon a straight path, lined with more modern buildings with sufficiently
substantial foundations not requiring the shoring up of older buildings.

Douglas A. Willinger
Takoma Park Highway Design Studio