s ▁at ▁Nich ol son , ▁Pennsylvania ▁and ▁Mart ins ▁Creek , ▁Pennsylvania , ▁were ▁built ▁of ▁rein for ced ▁concrete . ▁The ▁T unk h ann ock ▁Vi ad uct ▁at ▁Nich ol son , ▁the ▁line ' s ▁names ake , ▁is ▁considered ▁to ▁be ▁the ▁world ' s ▁largest ▁concrete ▁structure . ▁ ▁Bu ilt ▁with ▁approximately ▁ ▁of ▁concrete , ▁its ▁ten ▁sp ans ▁go ▁ ▁below ▁ground - level ▁to ▁bed rock , ▁making ▁the ▁center ▁span ▁of ▁the ▁bridge ▁effectively ▁ ▁tall . ▁Over ▁the ▁years , ▁Nich ol son ▁Vi ad uct ▁would ▁become ▁a ▁symbol ▁of ▁the ▁engineering ▁accomplish ments ▁of ▁the ▁L ack aw anna . ▁ ▁The ▁Nich ol son ▁C ut off ▁was ▁used ▁for ▁trains ▁of ▁the ▁Del aware , ▁L ack aw anna ▁and ▁Western ▁Rail road ▁and ▁later ▁used ▁for ▁trains ▁of ▁the ▁Er ie ▁L ack aw anna ▁Railway , ▁Con ra il , ▁Del aware ▁and ▁Hudson ▁Railway , ▁Gu il ford ▁Rail ▁System ▁( now ▁Pan ▁Am ▁Rail ways ), ▁New ▁York , ▁Sus que h anna ▁and ▁Western ▁Railway , ▁Canadian ▁Pacific ▁Railway ▁and ▁Nor folk ▁Southern ▁Railway . ▁▁ ▁The ▁Nich ol son ▁C ut off ▁was ▁opened ▁as ▁a ▁rail ▁line , ▁however ▁it ▁became ▁a ▁rail road ▁segment ▁when ▁it ▁became ▁part ▁of ▁the ▁Del aware , ▁L ack aw anna ▁and ▁Western ▁main ▁line . ▁Currently ▁as ▁a ▁rail road ▁segment , ▁the ▁Nich ol son ▁C ut off ▁served ▁as