Mait001 wrote:

It is also the complete lack of foresight and advance preparation when
building the original line, and then the T4 line that irks me.

There are many places with an irkable lack of foresight and advance
preparation (most notably Cutty Sark, where they built the platform too
short) but this is not one of those instances. The problem at Heathrow
is that they got the forward planning WRONG - other factors resulted in
the decision to build T5, making the advance preparation useless. How
could the engineers doing the planning avoid this? Do you think they
should make provision for every conceivable future plan, even the
mutually exclusive ones?

I think that would work out far more expensive than making no advance
preparation!

Let me give you an example. In the late 1960s/early 1970s, my father was a
civil engineer working for the London Borough of Hounslow. He was responsible
for rebuilding Stanwell Road, a road connecting the Great South West Road to
the cargo area of Heathrow Airport. At the time, there were vague rumblings
about building a rail link to Heathrow from Victoria. In the end, it was
abandoned because it would have cut through Buckingham Palace Garden.

What route would it have taken?

Why was Buckingham Palace Garden considered such an obstacle?

With that possibility in mind, however, he ensured that there were culverts,
diverted drainage etc., and indeed an opening beneath Stanwell Road (that is
there, unused, to this day) so that this could have been used by the railway
line if ever it was built.

Is it just under Stanwell Road itself? Or does it continue on under
Bedfont Road?

That would have ensured virtually no disruption to
Stanwell Road had that line been built.

But wouldn't the alternative (building it with a TBM) have the same
effect?

That is called foresight and forward planning that is so patently missing now.

With the Heathrow terminals in their current locations, is their any way
this piece of forward planning could now be exploited?