Railroads in North America are often classified into Class 1, Class 2 and Class 3 in terms of size. The classification has always been by means of annual operating revenue; the exact revenues required to be in each class have varied through the years since they have adjusted for inflation. There was a time when one million dollars annual operating revenue was the definition, but that was back when a million dollars was real money.
Currently, a Class 1 railroad has an operating revenue exceeding $255.9 million. The exact setting of the cut-off figure has always been as much a political thing as anything else; there have always been rumors of the powerful Class 1 companies voting to increase the cut-off to deny an upstart membership of their exclusive "club".