The collision was reported around 11 a.m. near McBride and Terry lanes.
Power lines were pulled down and initially 5,845 customers in the area were without power, PG&E spokesman JD Guidi said.
As of 12:27 p.m., only about 2,000 customers remained without power.
There is no estimated time when power will be restored for those customers, he said.
Repair crews have responded to the area, he said.
Police said McBride and Terry lanes are closed because of the traffic accident.
Other intersections without functioning traffic lights are to be treated as four-way stops, police said.
The outage is mostly affecting neighborhoods in northwest Santa Rosa, police said.