was designed to ease maintenance and to improve reliability. The cars used fabricated bogies with air suspension, unlike previous cars in the M series. M6 series As part of the MTA's 1987 Capital Program, 60 additional M4s would have been ordered to accommodate increasing ridership. This number was revised down to 48 in its February 1989 amendment, with 30 to be purchased by CTDOT, and 18 by the MTA. The December 1990 amendment changed the car order to a separate contract, the M6 series cars (9000-series). Similar to the change with the proposed purchase of M2 cars, the decision was made to purchase improved models following a reassessment of fleet requirements. The contract called for 39 cars, with an option for 9 more cars, and was awarded to Morrison-Knudsen in August 1990 for $91.5 million. Work was scheduled to begin 1991, and continue until early 1993. Nearly identical to the M4s, these cars were completed at Hornell, New York with body shells from Mafersa. Morrison-Knudsen was the last American builder of railcars, and heavily underbid on contracts, including on this contract, to gain a large share of the market. Morrison-Knudsen had almost no experience in the design of passenger railcars, and did not build a prototype for the M6. As a result, the first cars were rejected by Metro-North. In April 1995, the M6s were delayed by 18 months; only 12 cars were accepted in 1994, with the rest scheduled to be put into service in 1995. The M6s featured distinctive chimes that sounded whenever the doors were closed, a feature that did not exist on the M2s or M4s. The M6s also had black framed windows, giving them the illusion of being larger than the windows on the M2s and M4s. The M6s were also commonly referred to as "triplets". Retirement and replacement The M2s, M4s, and M6s were replaced, retired, and scrapped between 2012 and December 2018 as new M8 railcars entered service. In May 2014, Metro-North retired the bar cars, with the last one departing Grand Central Terminal on May 9. Since then, there have been several proposals to reintroduce bar cars by retrofitting the new M8 fleet. All M4/M6s were removed from service by July 2015. In November 2016, it was announced that the last 36 M2s would also be replaced by additional M8 cars beginning in 2019. The M2s were finally removed from service at