▁S . ▁C rid leb augh . ▁Form ally ▁titled ▁Br id ges ▁and ▁T unn els ▁of ▁Al leg hen y ▁County ▁and ▁Pitts burgh , ▁PA , ▁p gh brid ges . com ▁has ▁information ▁on ▁many ▁of ▁the ▁structures ▁of ▁the ▁Pitts burgh ▁area . ▁It ▁includes ▁detailed ▁histor ies ▁and ▁photograph s ▁for ▁hundreds ▁of ▁brid ges , ▁although ▁since ▁there ▁are ▁over ▁ 2 0 0 0 ▁brid ges ▁in ▁the ▁area ▁with ▁a ▁span ▁of ▁at ▁least ▁ 6 ▁feet , ▁not ▁all ▁are ▁included . ▁Cover age ▁is ▁based ▁on ▁historical , ▁architect ural , ▁or ▁engineering ▁significance . ▁ ▁For ▁many ▁of ▁the ▁bridge ▁articles , ▁C rid leb augh ▁has ▁searched ▁H A ER ▁documentation , ▁and ▁where ▁there ▁was ▁a ▁write up ▁or ▁report ▁in ▁. t if ▁format , ▁has ▁done ▁the ▁O CR ▁to ▁convert ▁it ▁to ▁text , ▁and ▁made ▁the ▁text ▁available ▁at ▁the ▁site . ▁ ▁References ▁ ▁External ▁links ▁ ▁about ▁p gh brid ges . com ▁page ▁from ▁the ▁site ▁ ▁Car neg ie ▁Library ▁of ▁Pitts burgh ▁lists ▁this ▁site ▁( second ▁link ) ▁on ▁its ▁" P itt s burgh ▁History " ▁page ▁as ▁a ▁resource ▁ ▁New ▁England ▁Institute ▁of ▁Technology ▁lists ▁this ▁site ▁( second ▁link ) ▁in ▁the ▁Historical ▁American ▁Br id ges ▁section ▁ ▁listed ▁as ▁resource ▁at ▁Struct ura e ▁ ▁Internet ▁Sc out ▁Project ▁( A ▁project ▁prom oting ▁math , ▁technology ▁and ▁engineering ) ▁ ▁of ▁the