A gunman was still at large on Monday after killing at least two people in a shooting spree on highways in and around Dallas, police and local media said.
Four separate shootings in less than an hour paralyzed traffic during the busy early evening rush hour, police said.
"We are working on the possibility that they may all be related," said Joe Harn, a police spokesman in the city of Garland, near Dallas.
A motorist was killed in Garland as his car was stopped at a traffic light. The gunman, reported to have been in a pick-up truck, then sped away.
Minutes later, there were three shootings on a major freeway leading into Dallas, leaving a truck driver dead.
Television footage showed traffic backed up as police closed off the crime scene around the 18-wheeler truck.