"Basil Jet" wrote in message
...
There's a tunnel under the Terminal 5 Roundabout. It seems that hardly
anyone going to or from any of the terminals would use it, so I'm
wondering why it's there - but then you could also say the same about the
less substantial underpass beneath the Terminal 4 roundabout. Why were
they built?

Guessing...

The existing perimeter road is possibly a key part of some safety plan or
other.

Paul S