. The Street railway journal . l to a point far enoughback on Selby Avenue at the high level to obtain a satis-factory grade. The total length of the improvement required in thegrade reduction is 1700 ft., including the tunnel and theapproaches. An approach, 230 ft. long, leads up to theportal of the tunnel at the bottom of the hill. The tunnelis 920 ft. long between portals and has an approach 320 length at the upper end. The lower approach is on acurve with a 500-ft. radius, but otherwise the alignment ofthe improvement is straight. The grade of the new trackis uniformly 7 per cent, as
. The Street railway journal . l to a point far enoughback on Selby Avenue at the high level to obtain a satis-factory grade. The total length of the improvement required in thegrade reduction is 1700 ft., including the tunnel and theapproaches. An approach, 230 ft. long, leads up to theportal of the tunnel at the bottom of the hill. The tunnelis 920 ft. long between portals and has an approach 320 length at the upper end. The lower approach is on acurve with a 500-ft. radius, but otherwise the alignment ofthe improvement is straight. The grade of the new trackis uniformly 7 per cent, as compared with per centon the old track. The approaches are so arranged thatafter the backfilling has all been placed, the street willagain be opened for traffic at practically the original grades. The approaches are between reinforced-concrete retain-ing walls, which vary from 3 ft. to a maximum of height. Where these walls are less than 6 ft. high theyare built as gravity-section structures. Above that height. ENTRANCE TO TUNNELthey are vertical, reinforced-concrete slabs, having a hori-zontal slab footing, and buttresses, 2 ft. wide and 6 on centers, on the rear side. The approach to thelower portal of the tunnel is at one side of the street, aroadway parallel with it connecting with the street overthe tunnel. The approach to the other end of the tunnelis at the middle of the street, but a 13-ft. drive was obtainedon each side of it, so, on the whole, the street is much im-proved for highway traffic as compared with the old ar-rangement. The tops of the walls of the approaches andthe portals of the tunnel are ft. above the street grade,and are surmounted by a 6-ft. ornamental-iron picket fence,to prevent accidents. The tunnel has a double-centered arch, with a span of23 ft. at the springing line and a rise of ft. The clear-ance at the center line of both tracks is ft., while thecenter height is 16 ft. 10 in. The arch is 24 in. thick at
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectstreetr, bookyear1884
