This part applies to all railroads except:
    
    
        
        (a) 
         A railroad that exclusively operates freight trains only on track which is not part of the general railroad system of transportation;
     
    
        
        (b) 
         Passenger railroads that operate only on track which is not part of the general railroad system of transportation and that operate at a maximum speed of 15 miles per hour over public highway-rail grade crossings; and
     
    
        
        (c) 
         Rapid transit operations within an urban area that are not connected to the general railroad system of transportation. See  49 CFR part 209, appendix A for the definitive statement of the meaning of the preceding sentence.