http://www.abandonedsubwaytunnels.com/

http://en.wikipedia.org/wiki/Abandoned_Pennsylvania_Turnpike

http://users.ameritech.net/chicagotunnel/tunnel3.html

http://www.rays-hill.com/turnpike/home.htm

http://www.pahighways.com/toll/abandonedturnpike.html

http://www.darkroastedblend.com/2007/07/abandoned-tunnels.html

http://www.cincinnati-transit.net/subway.html

http://www.infiltration.org/transit.htm

http://www.abandonedsubwaytunnels.com/subwaysite/subway_home.html

http://www.steamphotos.com/gallery/3405984_hFJN7

http://www.offroaders.com/album/centralia/links/Abandoned_Turnpike.html

http://www.abandonedohio.com/tunnels.html