Amtrak has issued a request for proposals seeking to rebuild its current diesel fleet or purchase a minimum of 50 to 75 next-generation locomotives.

The effort is aimed at replacing Amtrak’s aging national network diesel locomotive fleet used on long distance and some state-supported routes, Amtrak officials said in a press release.

“We expect that any new, state-of-the art locomotive will offer improved reliability, a smoother ride, improved safety features and make major contributions towards lowering emissions and we’ll also consider how rebuilding options of the current fleet could achieve these goals,” said Amtrak President and Chief Executive Officer Richard Anderson.

The rebuilt or new locomotives will primarily replace Amtrak’s P40 and P42 locomotives, some of which have been in service for more than 25 years. As part of the contract, Amtrak also seeks a multiyear maintenance agreement that would include technical support, spares, supplies and services.

Of late, Amtrak has been making changes to improve the rider experience. Examples of those improvements include refreshed trains, new fare structures, improved on-time performance, enhanced Wi-Fi connectivity, upgraded facilities and expanded onboard experience options, Amtrak officials said.

Additionally, the new or rebuilt locomotives are part of the railroad’s long-term upgrades, which include new Acela trainsets, ongoing improvements at New York Penn Station and the new Moynihan Train Hall and further development of stations in Chicago, Baltimore, Philadelphia and Washington, D.C., they said.