A power outage in northern San Rafael struck 20,000 customers Tuesday night, leaving numerous neighborhoods in darkness and cutting power to traffic lights.

The outage occurred shortly after 6 p.m. By about 6:45 p.m., power had been restored to about 8,400 of those customers, and there was no time estimate for the rest, said Pacific Gas & Electric spokesman J.D. Guidi.

The cause of the power failure was under investigation.

Contact Gary Klien via email at gklien@marinij.com.