The trolleys run autonomously using a Powered Up color sensor with Nonsense Wars' Pybricks color sensor code being the base of the code used to run the trolleys. The trolley designs are based on the Reading Street Railway's Osgood Bradley Trolley and single truck Birney. The system runs smoothly as long as the trolleys are going slow enough to process the stop and reverse color before they reach the end of the line. submitted by /u/BrickReadingRailroad [link] [comments]