Amtrak's Clockers were rush-hour trains, mainly serving the commuter and day-trip market to New York City. New Jersey Transit (NJT) passholders could ride Clockers, which were listed in the NJT timetable in addition to Amtrak's. They were popular with those who commuted to New York from Trenton and Princeton Junction, as they were faster and more comfortable than NJT trains.
Clockers made all, or almost all, Amtrak stops between 30th Street Station in Philadelphia and Penn Station in New York, unlike Amtrak's Regional trains which often skipped less-busy stations. The trains were unreserved, coach class only, and used Amfleet rolling stock.
The term Clocker originated with the Pennsylvania Railroad which had hourly train service between Penn Station in New York and Broad Street Station in Philadelphia. These were briefly rebranded as Acela Commuter in 2001 when Amtrak decided to use that moniker in conjunction with most trains along the Northeast Corridor. Following mass rider confusion between this service and the high-speed Acela Express service, the name was returned to Clocker in 2003.