A four-car, rush-hour crash on Highway 101 in Rohnert Park snarled traffic Wednesday and sent three drivers to the hospital.

The chain-reaction collision was reported at 5:25 p.m. in the northbound lanes just north of Rohnert Park Expressway.

The driver of a red Chevrolet Silverado pickup was traveling about 55 mph in the carpool lane when he switched back to the center travel lane just as traffic had slowed for congestion, according to CHP officer Jon Sloat.

The Silverado rear-ended an early 2000s Dodge Ram pickup, propelling it into and on top of a smaller, older model Chevrolet S-10 pickup in the lane ahead of it.

The Ram came to rest on top of the S-10, where it remained as emergency personnel scrambled to treat victims, sort out the mess of crumpled vehicles, and route traffic around the accident. The fourth vehicle, a Ford pickup, received minor damage.

The driver of the S-10, 33-year-old Brian Cooper of Santa Rosa, was transported to Santa Rosa Memorial Hospital with minor injuries.

The driver of the Silverado, 44-year-old Pedro Montef of Santa Rosa, suffered moderate injuries.

And the man at the wheel of the Ram, 70-year-old Cecil Harry of Rohnert Park, didn't appear to suffer major injuries in the crash, but may have suffered a medical emergency following it, Sloat said.

Shaun Newton, the manager of Mammoth Motorsports, was talking to a customer when he heard the crash right outside his Commerce Boulevard motorcycle shop.

"I didn't hear brakes or anything," Newton said.

The front end damage to the Silverado and the way the Ram crushed and rear of the S-10 before coming to rest atop it attested to the impact of the crash, he said.

In the wake of the accident, people appeared to be trying to get the unconscious driver of the Ram out of the cab, he said. When paramedics arrived they got him out and began CPR immediately, Newton said.

Traffic was backed up for more than a mile to Railroad Avenue from the wreck. All three northbound lanes were reopened at 6:43 p.m., Sloat said.

You can reach Staff Writer Kevin McCallum at 521-5207 or kevin.mccallum@pressdemocrat.com. On Twitter @citybeater.