In the second Divergent movie, Insurgent, the train is running on 2 tracks (the engine is using the two middle rails, and the wagons are running on the two side rail pairs). See the 9 seconds here from 0:37 and the top view:
How can this configuration be better than a regular train with twice the length? As I see, it would lose the benefits of having two tracks (they cannot pass a train coming from the opposite direction), the distance between the two tracks need to be constant for the engine (so probably all tracks had to be rebuilt as well), and the wagons can only be loaded from one side each. Limited station length is probably also not an issue (the cost of increasing the station length (or splitting the trains into two when arriving to the station) is probably comparable to rebuilding the stations to have equal distance between the middle rails and special switches for the different tracks).