A male bicyclist crossing Highway 12 at Boas Drive in east Santa Rosa was struck by a car and seriously injured Wednesday, snarling eastbound traffic through the area for several hours during the evening commute, authorities said.

Police Sgt. Chad Heiser said the cyclist was pedaling southbound across four lanes of traffic without a crosswalk or a signal when he was struck by an eastbound motorist who didn’t see him until it was too late to stop.

The driver, Oleksandr Kachan, a Citrus Heights resident, remained at the scene of the 5:09 p.m. crash and cooperated with the investigation, Heiser said. Kachan, 50, did not appear to be impaired in any way, police said.

The cyclist’s name was not available Wednesday night, Heiser said.

Emergency medical personnel who responded to the scene about 1,000 feet west of Calistoga Road treated the cyclist and then had him transported to a local hospital. Police said hospital personnel later said the man’s injuries, though major, did not appear immediately life threatening.

Investigation of the crash required police to close the eastbound slow lane for about two hours and both eastbound lanes for the final hour or so. The road reopened around 8:14 p.m.

The incident was one of at least four collisions on Highway 12 between Boas Drive and Melita Road during a one-hour period late Wednesday afternoon, though they did not appear to be related, authorities said. The others did not involve serious injuries.

You can reach Staff Writer Mary Callahan at 707-521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.