WASHINGTON — A new era of high-speed train travel is coming to the nation’s busiest rail corridor.

Federal officials on Friday announced a $2.45 billion loan to Amtrak for the purchase of state-of-the-art trains to replace the aging Acela trains that use the Northeast Corridor from Washington to Boston.

Amtrak plans to put the first of 28 new trains into service in about five years. Once they are fully deployed, officials expect the Acela to depart every half-hour between Washington and New York and every hour between New York and Boston. That should increase passenger capacity by about 40 percent, they said.

While the new trains will not approach the speeds of some Asian and European trains, officials said they hoped that the new Acela would travel at 160 miles per hour in some places, up from 135 m.p.h. now. The trains will theoretically be able to go faster than 160 m.p.h., though that would require a huge upgrade of the track system.

Vice President Joseph R. Biden Jr., a longtime Amtrak supporter who frequently travels by train between Washington and his home in Delaware, announced the loan at the station in Wilmington that is named in his honor.