A San Francisco man was killed Tuesday just south of Calistoga when his bicycle drifted into the path of a passing vehicle, the CHP said.

Thomas Battat, 50, was southbound on the shoulder of Silverado Trail near the Clover Flat Landfill around 1:40 p.m., the CHP said. For reasons unknown, he drifted into the travel lane and was struck by a southbound Chevy Impala, driven by Alvaro Ayala, 39, of Napa.

Battat suffered serious injuries and was taken to St. Helena Hospital, where he died a short time later, police said.

Ayala was not injured and the CHP release made no mention of charges being filed in connection with the crash.

Police said there is no indication that drugs or alcohol played any role in the accident.