"On the siding" is a phrase commonly used to describe railway cars or trains that are parked to the side of a track. There are several other synonyms that can be used to describe this scenario, including "on the spur," "in the yard," "on the sidetrack," and "in the shunt." The phrase "on the spur" is used to describe a track that branches off from the main track, while "in the yard" refers to an area where trains are sorted and stored. "On the sidetrack" is a general term for any track that runs parallel to the main track, and "in the shunt" is a British term that refers to the process of moving a train from the main track to a sidetrack.