>The Cahill Expressway loop tunnel would have to be well
> below the tramway tunnels, or it would have had to cut
> through the railway tunnels as well, because the road goes
> uphill as it curves around to the tollgate area on the bridge
> approach.
<sigh>
If you actually look at the nature of the Cahill expressway "tunnel"
you will see that the actual tunnel bore part does not start at the
edge of the bridge toll plaza roadway. There is a high cut on the
Circular Quay side which goes in probably 20 metres or so under the
toll plaza before the tunnel bore part commences. It runs up to near
the toll plaza roadway level. The top part of the cut carries a bunch
of air ventilation equipment and other services for the Cahill tunnel
attached to its walls, so you can't see what is in there but that is
where the tram tunnels were broken.
If you look at the cut in comparison to the level of the tram tunnels
at the exit from the car park in Cumberland St (which has steepish
grade from the tunnel up to street level) and the portals at Argyle
St, the level of the tram tunnels at cut point is fairly easy to work
out.
The arrangements on the Observatory side of the Cahill tunnel, where
the North Shore line Rail tunnels are located are quite different and
the road is actually at a lower level there than it is on the Circular
Quay side, where it is still descending from the elevated roadway
structure.
Cheers,
Bill
Bill Bolton
Sydney, Australia