Authorities are investigating how a baby boy was left by the side of a highway Saturday in eastern Oklahoma City.The driver of an Abba House of Worship church van spotted the three-month-old baby about 3 p.m. Saturday. The baby was lying in a car seat about 10 feet from the right shoulder of Interstate 40 near Triple X Road, police said.Emergency workers reported the baby could not have been outside more than 30 minutes and was healthy and appeared well cared for prior to being left. The boy is now in state custody.Master Sgt. Gary Knight said a birth certificate, a Social Security card and about $5,500 cash were found in and around the car seat. Police were able to locate the mother through relatives in Texas. The mother was taken to a hospital for observations."It's not clear what led her to leave the baby out on the side of the road but it is certainly something our investigators are looking at," Knight said.