WEST, Texas—A man, woman and her two toddlers were hit by a vehicle and killed while walking on an Interstate 35 frontage road after their pickup broke down, authorities said.

Just before 10 p.m. Thursday, the four left the pickup and began walking on the two-way frontage road when a sport-utility vehicle came over a small hill and slammed into them from behind, hurling their bodies about 100 feet, said Senior Cpl. Charlie Morgan of the Texas Department of Public Safety.

The victims were identified as Brandee Thorpe, 20; Austyn Fontenot, 2; and Kinzee Fontenot, 1; all of Hillsboro; and Gregory Howell, 25, of Robinson. Thorpe is the mother of the two children, but it’s unclear if they are related to Howell, Morgan said. The adults appear to have been carrying the children, he said.

Although the interstate is slightly illuminated by headlights, neither it nor the frontage road has street lights, so the area—near the town of West about 15 miles north of Waco—was very dark, Morgan said.

Charges will not be filed against the driver, Morgan said.

“She was on them before she knew it ... and best we can tell she wasn’t speeding,” Morgan said Friday.