A single-vehicle crash early Saturday morning sent a Roanoke teen to the hospital with what police described as “severe injuries.”   Roanoke County police say 19-year-old Daniel Maloney was injured at about 3:00 a.m. in the 7500 block of Countrywood Drive, just off Bent Mountain Road/ Route 221.   Police say the car left the road, struck some mailboxes and hit a tree.   Roanoke County Fire and EMS took Maloney to the hospital.   Police say alcohol or drugs may have been involved, and they say weather may have been a factor in the crash.