 By the 1920s, SCGX was doubling annually and had emerged as the "fastest growing grain market in the world"; transacting 22 million bushels in 1928 (valued at $336 million in 2018), resulting from its location in the heart of the Corn Belt and self-imposed standards before the Grain Standards Act of 1916 including species admittance and non-mixing.However, its growth was limited by shipping rates.With the trucking industry and Interstate Highway System not yet developed, SCGX was constrained by monopolized railroad rates, primarily by the Great Northern Railway.