In message , Roland Perry
writes

Are those the tunnels that are currently used by taxis, and have a
"loading gauge" hanging over the entrance? Or are the service tunnels
in addition to those?

It looks like it. A proposed route is shown on page 3 of ...

http://www.atsltd.co.uk/media/casest...se_studies.pdf

Page 4 shows (somewhat surprisingly) that it is possible to fit four
people-mover tracks inside one service tunnel - although it doesn't
explain what will be done with the displaced taxi traffic! I wonder if
there might be room to retain a taxi-way below the upper pair of tracks?

The maps on pages 59-62 of the Heathrow Masterplan (big download) ...

http://www.heathrowairport.com/asset...MasterPlan.pdf

show more extended systems, with different routes, to take account of
the third runway proposal.

--
Paul Terry