SAN FRANCISCO --

A doctor on his way to work was killed and four people were hurt Thursday in a crash involving a big rig and a UCSF shuttle bus in San Francisco's Hayes Valley neighborhood, a collision that a witness said was caused by the shuttle running a red light.

The crash happened at Octavia and Oak streets at 6:20 a.m. when a 2007 Peterbilt tractor-trailer truck carrying four cars collided with the Ford shuttle bus taking UCSF employees to San Francisco General Hospital, police said.

Dr. Kevin Allen Mack, a passenger on the shuttle bus who kept an office at San Francisco General, was ejected from the vehicle and ended up being pinned underneath the big rig, police said.

Father of 2 children

Mack, 52, a married father of two young children who lived in San Francisco, was pronounced dead at the scene. He was a psychiatrist who graduated from the University of Hawaii School of Medicine in 1994 and completed his residency in psychiatry at Harvard University before joining the UCSF faculty in 2000.

Three of the 15 people on the shuttle bus, two women and a man, suffered non-life-threatening injuries. One of the injured is 85 years old, but officials did not identify the person.

The shuttle bus driver, a man whose name was not released, suffered minor injuries. The 15-year university employee has been placed on paid administrative leave pending the outcome of a police investigation, said UCSF spokeswoman Elizabeth Fernandez.

Under investigation

The big-rig driver was unhurt.

The truck was traveling north on Octavia and the shuttle bus was heading east on Oak when the collision happened, authorities said. The cause of the crash is under investigation.

The big rig is leased to Mag Transportation LLC of Inman, S.C., and is operated and owned by Viktor Shkoda, 30, of Massachusetts, said a company dispatcher.

Shkoda called the company after the crash, saying he had the green light and that the shuttle bus had come from "out of nowhere," said the dispatcher, who asked that his name not be used.

Eyewitness

Colleen McClain of Pittsburg said she had been two cars behind the big rig on Octavia and that they had the green light.

"The UCSF shuttle ran the light and hit the big rig," McClain said.

The shuttle bus did not have seat belts. Fernandez said the safety devices are not required, which police confirmed.

In a statement, UCSF Chancellor Susan Desmond-Hellman expressed her "deep sorrow and sympathy to Dr. Mack's family and friends."

Mack was an associate clinical professor of psychiatry at UCSF. His clinical expertise was in bipolar and psychotic disorders, and his research interests included neural networks and cognitive processes.

"He was such an amazingly creative, innovative, inspiring physician and medical educator," said Dr. Ann Stevens, director of a UCSF-UC Berkeley program that Mack helped lead. "Whoever he touched in the medical world or the community knew what a special person he was."

'Real humanitarian'

His sister-in-law, Megan Nitta, 40, of San Rafael called Mack "a real humanitarian. He was an amazing person. We lost an incredible person today."

Naoki Nitta, 43, Mack's husband of three years, said he "had a sense of purpose that was way above himself."

Mack leaves behind two children, a 7-year-old daughter and a 4-year-old son.

On UCSF's website, Mack wrote, "I'm basically an educator at heart, who chose medicine as a career after deciding that gay teachers weren't going to be 'safe' professionally for several decades.

"Although I enjoy my clinical work," Mack added, "my greatest joy comes from helping people use their own sense of wonder and inquiry to find and fuel their passion - whether that be in science, arts or something else entirely."

Second fatal crash

Thursday's crash was the second fatality involving a UCSF shuttle bus in the past year. In November, a shuttle bus struck and killed 65-year-old Nu Ha Dam as she was crossing Geary Street at Leavenworth Street.

Criminal charges are pending against the driver in that incident, Fernandez said.