I am purchasing a 89 foot rail flat car and want to put a bridge in on my lane that will last a lifetime.   I am spanning about 50 feet therefore I have about 20 feet of bridge on each bank.   I plan to cross it with loaded semis from time to time also.  
       
        Question is what should I put the bridge onto for a foundation and how should I do it??       
      
      I plan to hire a contractor with a large excavator for the project.              I'm thinking lots of concrete and some sort of cribbing to keep the banks from washing out underneath overtime...    Any and all ideas appreciated! TIA.