Complex sentence: Most of Amtrak's Princeton Junction service prior to 2005 was "Clocker" service commuter traffic to New York, Newark, or Philadelphia; since October 28,2005, the Clockers have been replaced by NJT trains that run only as far south as Trenton.
Split into simpler sentences: Most of Amtrak's Princeton Junction service prior to 2005 was "Clocker" service commuter traffic to New York, Newark, or Philadelphia. Since October 28,2005, the Clockers have been replaced by NJT trains that run only as far south as Trenton.