A pedestrian trying to cross Interstate 93 in Boston was struck by a vehicle and seriously injured Thursday night, State Police said. The 45-year-old woman was taken by Boston Emergency Medical Services to Boston Medical Center, Trooper Nicole Morrell said, although it was unknown whether her injuries were considered life-threatening. The woman was hit just before 9 p.m on the southbound side of the highway near Columbia Road, State Police said. It was not clear what kind of vehicle struck the woman. The right two lanes were closed while police investigated, Morrell said.