SS meaning in Regional ?

The Sand Springs Railway (reporting mark SS) is a class III railroad operating in Oklahoma. It began in 1911 as an interurban railway providing passenger service between Tulsa and Sand Springs. It soon developed a freight hauling business between the two cities. Passenger service was discontinued January 5, 1955, but the railroad has continued to operate until the present. On May 28, 2014, it was announced that the railroad would be acquired by OmniTRAX, with operations commencing no later than July 31, 2014

It provides freight rail service between Sand Springs and Tulsa over a 32-mile route. The company primarily hauls steel, pulp, scrap iron, scrap paper, petroleum products, plastic, and lumber. It interchanges with the Union Pacific Railroad, BNSF Railway and the South Kansas and Oklahoma Railroad.