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PHILADELPHIA (CBS) – A Philadelphia Highway Patrol officer remains in critical condition following surgery after his motorcycle was struck by a minivan in Northeast Philadelphia on Thursday. Doctors say the next 72 hours are critical as they “aggressively monitor” his condition.

Philadelphia Police Commissioner Richard Ross told the media Friday morning Officer Andy Chan’s condition has not changed since surgery.

“It’s good news in the sense it’s not a lot of change, because of the significant injury that he sustained,” said Ross. “Believe it or not, that’s actually a good sign right now. I just spoke to the trauma surgeon and she indicated the next 72 hours are critical for Andy, and she’ll be doing what she dubbed as ‘aggressive monitoring,’ and that’s literally minute-by-minute to check on swelling on his brain.”

A minivan struck Chan and threw him from his motorcycle around 5:45 p.m. Thursday on Rhawn Street near Rowland Avenue. Paramedics rushed Chan to Jefferson-Torresdale Hospital with a critical head injury. He underwent surgery and remains in the ICU.

Authorities say the 79-year-old driver who struck Chan did stay at the scene. Ross says it appears to have been a tragic accident, so the man is not expected to face charges.

“There’s no indication of impairment. It just seems like an absolutely tragic accident that we’re hopeful will end in a very positive way,” said Ross.

Chan, who has been on the force for 24 years, was on his way to work at the time of the accident.

“We are just ever so hopeful that he is going to survive his injury and this traumatic ordeal. Someday he will join us again, he will don that uniform.

“He is one heck of a police officer. He is well known and well regarded in this police department,” Ross said.

The cause of the accident is still being investigated.