Complex sentence: The PRR extended its railway electrification program to Potomac Yard in 1935, marking its southernmost point--the Penn Central segment of the famous Tropicana Juice Train operated from here.
Split into simpler sentences: The PRR extended its railway electrification program to Potomac Yard in 1935, marking its southernmost point. The Penn Central segment of the famous Tropicana Juice Train operated from here.