Commuter trains to Northern Virginia will be longer than usual to accommodate the anticipated mid-day rush as federal workers head home early, but there will be no additional trains, a spokesman said.

Virginia Railway Express will operate eight-car trains on the Fredericksburg line’s Train 301 and the Manassas line’s Train 325. Trains 303 and 327 also will have longer trains than usual, said VRE spokesman Mark Roeber. Eight-car trains have 1,200 to 1,300 seats, he said.

Roeber said VRE couldn’t run additional trains because of operating agreements with CSX, Amtrak and Norfolk Southern that limit VRE trains to the current schedule. Other rail companies use the tracks mid-day, he said.

“Based on our available time slots, we’re doing what we can to increase capacity,” Roeber said.

Roeber said VRE expects to be able to accommodate all passengers Tuesday afternoon but said crowding could become a problem by the time the trains reach Alexandria.

About 65 percent of VRE passengers are federal workers, Roeber said.

He said VRE plans to run full service on Wednesday but will make a final announcement on that around 6 p.m. Tuesday.