The eight new M-8 cars were put into service on Tuesday for the Metro-North rail line.
The first train left Stamford at 10:30 a.m. and arrived at Grand Central Terminal in New York at 11:36 a.m.
Connecticut has ordered 380 Kawasaki cars to replace the aging fleet. They cars will run on the commuter line between New Haven and New York City.
The first batch of trains had been delayed because of problems that cropped up during the testing period, frustrating many commuters.
"This testing took over one year to ensure that the M-8 will provide quality service for its 30 year life. We plan to put more of these cars into service as soon as they complete individual quality assurance testing," said Metro-North President Howard Permut.
The initial order was placed with Kawasaki Rail Car, Inc. in August 2006, at a cost of $761 million, shared 65 percent by the State of Connecticut and 35 percent paid by New York State's Metropolitan Transportation Authority.
Connecticut Gov. Dannel P. Malloy says the 63,000 commuters who use the line daily can expect all 380 cars up and running by 2013.
In a related matter, Metro-North is resuming its regular, full New Haven Line schedule on Monday, March 7. A reduced schedule was implemented on February 7 to give mechanics time to repair the winter-crippled fleet of older M-2, M-4 and M-6 cars.