It happened about 5:35 p.m. Sunday.
Troopers say 73-year-old Bernice Wastler of Rehoboth Beach was driving north on the highway when 34-year-old Kelley R. Oram of Rehoboth Beach was trying to walk across the highway.
Police say Oram is in critical condition at a local hospital. Wastler was taken to another hospital with non-life-threatening injuries.
The accident is under investigation.