Northbound Interstate 95 is closed at Route 100 in Howard County because of a tractor-trailer overturning about 3 p.m. Thursday, police said.
The crash will likely keep the highway closed through the evening rush hour, Maryland State Police said in a statement shortly before 5 p.m.
Traffic is backed up to around Exit 35A onto Route 216.
Drivers should avoid the area south of Elkridge, police said, because all four lanes are closed to traffic. State Highway Administration staff are detouring northbound vehicles onto Route 100.
The semitrailer, carrying junked vehicles, overturned, and some of the vehicles fell onto the highway causing two other, minor crashes.
Police said that no serious injuries were reported.