Waxahachie police are increasing presence along State Highway 77 after drivers reported they were shot at while traveling northbound.
Bullets struck a minivan and three trucks between 6 p.m. and 7 p.m. Monday.
A 13-year-old girl who was riding in the passenger side of one of the vehicles was struck by bullets in the foot and was rushed to a hospital.
Police Chief Charles Edge said everyone who plans to drive along the route to be on alert until the shooter is caught.
"We are not looking at it like an accidental or negligent act," he said. "We are investigating as if it was someone targeting cars going down the highway."
Authorities said the gunman used a pistol and may have hid while shooting at vehicles along the highway.
Police will look over the vehicles that were shot and interview the victims again later this week.
Officers plan to increase patrols around the area where it happened.
Anyone with information on the shootings is asked to contact Waxahachie police at 972-937-4320.