Mrs. Allen, 35, was driving north on I-95 when her 2005 Ford Expedition went under a parked tractor-trailer with no load around 7:51 a.m., as she exited the highway at Route 22 in Aberdeen, according to Maryland State Police.
Mrs. Allen was the wife of Deputy Chris Allen of the Harford County Sheriff's Office.
Sgt. E. Torres, with the Maryland State Police JFK Barrack, said Saturday she was killed on impact.
State Police, as well as the Aberdeen Police Department and the Aberdeen Fire Department responded to the scene.
Mrs. Allen was alone in the vehicle and the driver of the tractor-trailer was uninjured, Torres said.
The exit ramp was closed for about two hours, Torres said. The accident disabled the rear tire of the tractor-trailer.
In a news release issued Monday, State Police said the Ford Expedition SUV "for unknown reasons" drove onto the shoulder of the northbound Aberdeen exit 85 ramp on Interstate 95 "striking the rear of a tractor-trailer unit parked on the shoulder of the ramp."
"Maryland State troopers from the JFK and Bel Air Barracks are conducting a detailed reconstruction of the crash as they continue the investigation," the release stated.
Funeral arrangements for Mrs. Allen are being handled through McComas Funeral Home in Abingdon.
According to the McComas website, visitation for Mrs. Allen will be at the funeral home at 1317 Cokesbury Road in Abingdon, Friday from 2 to 4 p.m. and 7 to 9 p.m.
The funeral service will be Saturday at 11 a.m. at Bethel Apostolic Church at 21 N. Earlton Road in Havre de Grace. Burial will be in Baker Cemetery in Aberdeen.
Mrs. Allen's death was the 29th on Harford County highways in 2012.