SEMTA engine 521 pulls its commuter train northbound towards the Pontiac station - c. 1970's.  The photograph was taken under the southbound signal bridge near Yellow Cab Yard.  Yellow Cab Yard served the General Motors Truck and Bus plant in Pontiac.  It is so named because taxicabs were manufactured there years ago, as well as school buses.  Like so many things on a railroad, the name has stuck long after cab production stopped.  [Charlie Whipp collection].