Tunnels

http://ca.finance.yahoo.com/photos/transport-of-the-future-a-look-back-slideshow/transport-of-the-future-a-look-back-photo-1376505093706.html

http://blog.modernmechanix.com/chicagos-freight-subway-does-the-work-of-5000-trucks

http://www.popularmechanics.com/technology/engineering/architecture/4343590#slide-1

http://www.bing.com/search?q=+secret+tunnel+system%2Cmodern+mechanix&qs=n&form=QBRE&filt=all&pq=secret+tunnel+system%2Cmodern+mechanix&sc=0-0&sp=-1&sk=&cvid=8176cc2f0a0b4e13876940c643d8b77a