The pre-tunnel trolley street line, which ended in 1984, ran from the long-removed Clearview Loop stop on Alfred St. (Mt.

[1] The difference with NATM lies in the means of support required to maintain the rock cavity and the configuration of the tunnel structure.

With conventional tunneling, support of the rock cavity consists of a rib cage framework of steel beams and horizontal wooden planks.

A reinforced steel concrete lining is added to create a perfectly shaped tunnel.

This is done by lining the tunnel cavity with several thin layers of shotcrete, concrete that is blown on under air pressure.