Complex sentence: In May 1966, Colonial began phase one of an expansion project which consisted of 18 intermediate booster stations which added horsepower to the system and in turn allowed more product to flow through the mainline between Selma, North Carolina and Greensboro, North Carolina.
Split into simpler sentences: In May 1966, Colonial began phase one of an expansion project to add 18 intermediate booster stations to add horsepower to the system. This resulted in increasing product flow through the mainline between Selma, North Carolina and Greensboro, North Carolina.