ine ▁Lane ▁( off ▁To ole y ▁Street ) ▁on ▁the ▁south . ▁In ▁ 1 8 6 9 ▁a ▁ ▁circular ▁tunnel ▁was ▁d ug ▁through ▁the ▁London ▁cl ay ▁using ▁a ▁cast ▁iron ▁shield , ▁an ▁idea ▁that ▁had ▁been ▁pat ented ▁in ▁ 1 8 6 4 ▁by ▁Peter ▁W . ▁Bar low ▁but ▁never ▁built . ▁A ▁ ▁narrow ▁gauge ▁railway ▁was ▁laid ▁in ▁the ▁tunnel ▁and ▁from ▁August ▁ 1 8 7 0 ▁a ▁cable - h au led ▁wooden ▁carriage ▁convey ed ▁passengers ▁from ▁one ▁end ▁to ▁the ▁other . ▁This ▁was ▁une conom ic ▁and ▁the ▁company ▁went ▁bank rupt ▁by ▁the ▁end ▁of ▁the ▁year . ▁The ▁tunnel ▁was ▁converted ▁to ▁ped est rian ▁use ▁and ▁one ▁million ▁people ▁a ▁year ▁crossed ▁under ▁the ▁river , ▁pay ing ▁a ▁to ll ▁of ▁a ▁half pen ny . ▁The ▁opening ▁of ▁the ▁to ll - free ▁Tower ▁Bridge ▁nearby ▁in ▁ 1 8 9 4 ▁caused ▁a ▁drop ▁in ▁income ▁and ▁the ▁tunnel ▁closed ▁in ▁ 1 8 9 8 , ▁after ▁being ▁sold ▁to ▁the ▁London ▁H yd ra ul ic ▁Power ▁Company . ▁Today ▁the ▁tunnel ▁is ▁used ▁for ▁water ▁main s . ▁ ▁The ▁same ▁shield ▁method ▁of ▁construction ▁was ▁used ▁in ▁ 1 8 9 0 ▁to ▁dig ▁the ▁t unn els ▁of ▁the ▁City ▁and ▁South ▁London ▁Railway , ▁the ▁first ▁of ▁London ' s ▁elect r ified ▁" Tube " ▁rail ways ▁and ▁the ▁first ▁under ground ▁elect r ified