One passing loop is one slow-down and stop followed by one waiting for a train to pass followed by one acceleration. Many passing loops due to the need to make way for frequent passenger trains multiplies the loss in time. (BTW, the corridors where fast train service would be likely are in large part still double-tracked in the US, including the main trans-Appalachian lines.)

_{*Lunatic*, n.
One whose delusions are out of fashion.}