Two locomotives on the Capitol Corridor passenger rail service will soon be replaced by modern ones that are cleaner and more fuel-efficient.

The sleeker locomotives — U.S.-made by Siemens — promise to reduce particulate matter emissions from the old locomotives by 90 percent and nitrogen oxide by 80 percent, according to officials with the Capitol Corridor Joint Powers Authority. The locomotives also have regenerative braking systems that use energy from the traction motors during braking to minimize fuel consumption.

The new locomotives are expected to go into service sometime between now and June 1, when the current locomotives are required to stop operating.

The Capitol Corridor is an intercity rail service connecting Auburn and Sacramento to Silicon Valley, San Francisco, Oakland and Berkeley.