State Route 67 will be closed from 3 a.m. to 7 a.m. Sunday between Interstate 8 in El Cajon and Route 52 in Santee, while SDG&E crews move electrical transmission lines above the freeway, a Caltrans official said.
The eastbound I-8 off-ramps at Johnson Avenue and Magnolia Avenue in El Cajon will also be closed those hours.
Detours will be via surface streets, including Magnolia, Mollison and Graves avenues, Caltrans officials said.
Southbound 67 traffic can re-enter the freeway at Fletcher Parkway, and from there can reach I-8.
Caltrans crews will post signs to notify drivers of the detours.