In the 1980s I recall seeing SW engines on road trains quite often. Over the years I have read many theories for this, but as I thought about recently I figured this forum might have some insight. Can SW engines mu with road power (GPs and SDs)? One of the theories is that heavy trains needed more tracktive effort to get started, so the railroad would add an SW for starting and then it would "go offline" above 25 mph. Another idea was it was the closest engine to the train, and they just needed more HP. Finally and probably most realistically, it was off line and the railroad was just moving it from yard to yard. Can you expand on the usage of SW engines with road engines on road trains?