Firefighters battled a pre-dawn blaze Friday beneath the Laurel Street bridge on state Route 163 in Balboa Park.
The fire, of unknown origin, caused traffic to be shut down in a northbound lane for more than an hour after it was initially reported, shortly before 5 a.m.
A San Diego police officer, according to OnScene.TV, saw a male running away from the fire on the southbound side of SR-163.
Two engines from the San Diego Fire-Rescue Department responded to douse the flames.