JANESVILLE, Wis. -- The Rock County Sheriff's Department is investigating a two-vehicle crash Friday afternoon that left one person dead and four injured.

Authorities said the crash occurred just outside Janesville's city limits at the intersection of Highway 11 and U.S. Highway 51 at about 2 p.m.

Authorities said Debra Anderson, 47, of rural Orfordville, was traveling south on U.S. 51 in a Ford Tempo when she failed to stop at a red traffic light and was broadsided by a Dodge Ram pickup truck that was traveling west on Highway 11.

Sheriff's officials said the pickup truck rolled onto its side, and Anderson's car hit a traffic light, which then fell on top of the pickup.

Anderson died at the scene. Authorities said her 9-year-old granddaughter, who was a front seat passenger, had to be extricated from the car. She was taken to Janesville's Mercy Hospital and then flown to Milwaukee's Children's Hospital.

Sheriff's officials said the occupants of the Tempo did not appear to be wearing safety belts.

Authorities said the 35-year-old driver of the pickup and his 4-year-old and 14-month-old sons were treated at Janesville's Mercy Hospital for unknown injuries.

Investigators said it is not yet known if alcohol was a factor in the crash. They said speed does not appear to be a factor.