Additional series of cars bearing the Comet name, based on the original design, have since been built by Bombardier Transportation and Alstom.

These cars were the first of the Comet series, built by Pullman Standard in 1970–73 for the New Jersey Department of Transportation and used the Erie-Lackawanna Railroad's diesel-hauled commuter services.

These were considered state of the art at the time, due to their all-aluminum body shell construction as well as their use of head-end power (HEP).

The Comet I cars have become popular with western commuter lines as the low door setup is compatible with the low-platform stations in use.

FrontRunner retired their Comet I cars on April 18, 2022, citing increased maintenance costs and low ridership;[1] they were put up for auction in October 2022, lasting until November 2022.

These cars have been overhauled by AAI Corporation and Alstom between 1999 and 2003 to make them aesthetically and technologically similar to the Comet IV series and are now compatible with later equipment.

Shoreliner I and II coaches, purchased by Metro-North and the Connecticut Department of Transportation for use on non-electrified territories east of the Hudson River, are variations without long doors.

The Comet III fleet was removed from revenue service between 2009-2010 and remained in storage until 2022, when it was decided to dispose of the cars as scrap.

[12] The Comet IV cars, delivered in 1996 and purchased for NJ Transit's new Midtown Direct service, are similar to the Comet III cars, except they have no door by the engineer's cab, have thicker black stripes along the window, exterior and interior LCD panels providing destination and station information, a new interior color scheme, and power operated saloon doors.

The major external differences are a stainless-steel exterior, larger windows, and visible, roof-mounted air conditioning units.

In 2008 the California Department of Transportation (Caltrans) purchased 14 Comet IB coaches from NJ Transit for $75,000 per car to relieve overcrowding on the popular San Joaquin route.

[13] Caltrans had planned to use the "Comet car" trainsets on trains starting in July 2013, but the refurbishing process took longer than expected.

[16] The Comet cars will eventually be replaced by new Siemens Venture trainsets, after which there are plans to move them to Southern California for use on other routes.

[17] On the night of June 27, 2024, six Comet railcars as well as two EMD F40PH NPCU cab cars were delivered to Los Angeles after being attached in Oakland to the Coast Starlight.