Fireball RR posted:Hi @prrjim my e-mail has been updated in my profile, thank you for letting me know. Quick question, If I'm modeling 1940's & 50's the interchange tracks would still be there but class 1's would normally be interchanging freight with themselves the majority of the time right? Their own switchers would deliver "the last mile?"
In that time period railroads did indeed [mostly] deliver the last mile with their own crews&equipment. The ICC, which was created to regulate the original railroad monopolies, was tasked with insuring that trackside businesses had access to shipping. Hence switching-jobs and local-freights. In 1980 the ICC was junked as were the old regulations insuring access. Also the old anti-monopoly regulations. Hence the rash of mega-mergers and the end of the switching-job and the local-freight (those services were often money-losers for the railroads but essential for small shippers).
The term 'interchange' means from one railroad entity to another. There was always major interchange among railroads. Chicago was pretty much a gigantic interchange yard because so many railroads end/started there. The California Zephyr "interchanged" twice to get from Chicago to Oakland. Burlington, D&RGW and then Western Pacific. Much/most of the freight tonnage of those three railroads also interchanged to get from origin to destination. What with the recent mega-mergers the four remaining mega-systems do pretty much interchange within themselves. 
