SAN FRANCISCO (CBS SF) – The driver of a University of California at San Francisco shuttle bus that collided with a big-rig on Octavia Boulevard Thursday morning may have ran a red light, police said Friday.

Witness reports indicate the shuttle bus driver may have ran a red light while traveling east on Oak Street shortly before the 6:20 a.m. crash, which killed Dr. Kevin Mack, a 52-year-old UCSF psychiatrist and associate professor, police Lt. Troy Dangerfield said. The crash remains under investigation.

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The shuttle was taking Mack and about 15 others to work at San Francisco General Hospital when it collided with a big-rig that was headed north on Octavia Boulevard at Oak Street in the city’s Hayes Valley neighborhood, Dangerfield said.

Mack, 52, was ejected in the crash and landed underneath the big-rig, which was carrying several cars. He was pronounced dead at the scene.

Three other passengers—two women and a man – suffered injuries in the crash and were taken to San Francisco General Hospital for treatment. The shuttle bus driver suffered minor injuries, but the driver of the big rig was not injured, Dangerfield said.

The three other victims ranged in age from 58 to 85 years old, and all were in fair or good condition Thursday, hospital spokesman Tristan Cook said.

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The big-rig suffered damage to its left front end. The front right side of the shuttle bus near the door was crushed inward and a side window was broken.

Mack is survived by his husband and their two children.

Supervisor Ross Mirkarimi, who represents the area in which the crash occurred, on Thursday noted that Octavia, which he called a “fabulous boulevard,” could be challenging for drivers, especially those unfamiliar with the city.

Mirkarimi also noted that seatbelts in the shuttle bus could possibly have helped save Mack and those injured in the crash.

The shuttle bus did not have seat belts, according to fire officials.

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