The woman, who authorities identified as 62 years old and possibly homeless, was found on the Encinitas Boulevard off-ramp of the north Interstate 5 at about 6:30 a.m., said CHP Officer Mark Latulippe.
The CHP shut down the off-ramp until about 8:55 a.m.
Officers believe the woman was struck by a vehicle. Debris located at the scene indicates the involved car may have been a Ford F150 truck or Ford Expedition SUV model from 1995 to 2002, Latulippe said.
Anyone with possible information about this incident is asked to call the CHP's dispatch line at 858-637-3400.