TIL there's a series of 70-foot-long concrete arrows that bisects the country longitudinally all the way from SF to NYC, all designed to direct aerial traffic. They are from the pre-digital age and were installed by the Federal government in 1924, coupled with light signals to guide the way.

http://weburbanist.com/2013/12/30/pointing-nowhere-mysterious-arrows-in-remote-places/



Submitted March 21, 2015 at 11:33AM by vitruv http://www.reddit.com/r/todayilearned/comments/2zs7qf/til_theres_a_series_of_70footlong_concrete_arrows/