. Shield and compressed air tunneling . K_ 29:0 - - Roqers Pass [^ 2G-o- >^ Severn TWO-TRACK TUNNELS. : >^ Bergen Hill, Erie Four-Track TunnelFOUR-TRACK TUNNEL 0 10 20 30 Fig. 11.—Cross sections of railroad tunnels—two- and four-track. SIZE AXD SHAPE OF TUNNELS 59 ft. and for three lines of traffic the width should be 28 ft. Fur-ther it has been concluded that the overhead clearance should be13 ft. 6 in. These dimensions, however, are local and depend on

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