A 21-year-old woman driving on southbound state Route 163 around 7:30 a.m. near Balboa Avenue was shot through her rear passenger-side door, likely by someone in another car, San Diego Police said Tuesday morning.For the purpose of investigating the crime scene, at about 11 a.m. the California Highway Patrol, with the assistance of Caltrans, shut down the southbound traffic lanes of SR-163 at the Interstate 15 split -- diverting traffic to southbound I-15. While drivers took detours, CHP investigators lined up across all four lanes and searched for clues that could lead them to the gunman. "They're going to be looking for anything, from match packages to shell casings anything they can find out of the ordinary that would be trace evidence of somebody being here," said former police officer Kevin LaChappelle. Two clusters of shell casings possibly connected to the shooting were found. One of the clusters was along the shoulder near Ronson Road and the other was found about a quarter mile south near the Balboa Avenue overpass. CHP investigators there were five shell casings found in each location. The casings appeared to be from a small caliber weapon. 10News showed pictures of the casings found on the freeway to gun expert David Miller. "The casings in these pictures appear to be .22 caliber," said Miller. Miller said the bullet that hit the woman's car was from a gun that was more powerful. "I don't think the .22 made the hole in that vehicle because the hole is quite a bit larger," he said. "The hole indicates something like a 9 mm [gun]." LaChappelle said the placement of those shell casings indicates the shots were fired from a stationary position and not from a moving car. However, based on the bullet hole and the trajectory of the bullet, the shot was fired from another car, according to SDPD. CHP investigators said the car was possibly about half a car length back and one lane over from the victim's vehicle when the shooting happened.Miller agrees. "The paint chips on the left side of the hole are fairly intact but on the other are not, so that's going to indicate the trajectory of the bullet came at an angle going forward," he said. CHP investigators also canvassed the auto dealerships and other businesses along Kearny Mesa Road and were looking for anyone who might have seen or heard the shots. Sources close to the investigation told 10News they are also questioning gang members to see what they know."They're going to go for anything they can," said LaChapelle. "This could be young people, you know, a group of kids. It could be a gang initiation. There's a number of things that it could be so they're not going to leave any stone unturned."The closure of SR-163 was initially expected to last approximately two to four hours but authorities re-opened the roadway around 1:45 p.m.Authorities said the female driver was in the fast lane of SR-163 when a bullet entered the door of her 2006 silver Toyota Matrix and went through the driver's seat before hitting her in the torso.The woman told police she felt pain in her abdomen but, apparently, was unaware that she had been shot until she was on her way to the University of San Diego, where she is enrolled as a student.The woman was taken to Sharp Memorial Hospital, where she underwent surgery, according to a California Highway Patrol officer. No hospital condition was made available. 10News learned doctors were not able to remove the bullet from the woman's side. The victim called her mother about 7:30 a.m. and, apparently unaware that she had been shot, told her she was having a hard time breathing, USD spokeswoman Pamela Gray Payton said. Her mother called for help seven minutes later, she said.After calling her mother, the wounded woman was met by paramedics about 50 yards away from USD's east campus entrance, Payton said, adding that the CHP erroneously said someone at the USD gate called for help.Paramedics determined that the woman had sustained a gunshot wound to the right rear of her torso."They saw some blood in her torso area and discovered that she had actually been shot," said SDPD Lt. Darryl Hoover. "She was transported to the hospital [and] at the time, she was conscious and breathing." Curious students walked by the damaged car, shocked that something like that could happen to a fellow classmate. "It's scary to think about driving to school," said USD sophomore Anna Ricci. "You never know what's going to happen to you." Police investigated her car on campus, with much of the focus on a bullet hole in the rear passenger door, according to authorities. The young woman's name hasn't been released yet but her car is registered to Elvira and Denzil Simmons of Escondido. Neighbors of the address that showed up on the car's license plate registration told 10News they can't imagine the young woman being a target. "She'd be one of those daughters that everybody would want," said a neighbor. "She's just a good kid. She goes to school every day." Investigators said they do not have any descriptions of the shooter or the vehicle involved. They have not yet determined the type of gun used in the shooting.