PORTLAND – The Amtrak Downeaster train soon will be adding new and faster trips between Portland and Boston, officials announced Monday.

The Downeaster will add a fifth daily round trip on the line beginning Aug. 17. The addition of a fifth trip had been anticipated after the completion of a $6 million track construction project that has been under way since last fall.

Under the new schedule, the Downeaster will no longer run a bus for its late-night trips on weekdays, using a train instead. On weekends, there will be five train trips rather than the current four.

The trips also will be five minutes faster than they are now. The 21/2-hour trips will be cut to 2 hours and 25 minutes; trips that are now 2 hours and 35 minutes will be cut to 21/2 hours.

The new schedule is expected to have a positive impact on the train’s ridership, said Patricia Quinn, executive director of the Northern New England Passenger Rail Authority, which manages the train service.