LADOTD has put together a publication highlighting the state's older bridges.
http://wwwapps.dotd.la.gov/administration/public_info/projects/docs_test/48/documents/Crossing_The_Bayou_Louisianas_Historic_Bridges_Publication.pdf (http://wwwapps.dotd.la.gov/administration/public_info/projects/docs_test/48/documents/Crossing_The_Bayou_Louisianas_Historic_Bridges_Publication.pdf)