RICHMOND (CBS SF) — The California Highway Patrol is investigating a shooting reported in the area of Interstate Highway 580 in Richmond Thursday afternoon.

A witness reported the shooting and the CHP closed the Canal Boulevard on-ramp to westbound Highway 580 at 2:53 p.m. to gather evidence, CHP officials said.

They discovered shell casings on the on-ramp but so far no shooting victims have come forward, CHP officials said. The on-ramp was reopened just after 5 p.m.

There have been at least three-dozen shootings on highways in Alameda and Contra Costa counties since last November, including a shooting on Highway 580 in Oakland on Wednesday that wounded two people.

However, there had been few shootings reported from June until October, when there were two shootings along Richmond highways.

© Copyright 2016 by CBS San Francisco and Bay City News Service. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.