CHICAGO (CBS) — A 21-year-old woman was killed, and at least four other people were injured Monday morning, when a charter bus crashed on the inbound Stevenson Expressway.

The driver of the Burlington Trailways bus – carrying 33 passengers from Omaha, Nebraska, to Chicago – told the company he swerved to avoid a pickup truck that veered into its lane, according to a statement from Burlington Trailways.

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Illinois State Police said the bus struck a construction arrow sign around 6:40 a.m.

��I could hear a boom. So you know when you hear a noise, you’re going to jump up. I had seen windows busted. It was three windows; on the passenger’s front side, then the window next to the stairs, then the back window, it was all open. A woman in the back had got injured real bad,” passenger Jessica Sanders said.

Police said 21-year-old Nicole Underwood, from Des Moines, Iowa, suffered fatal injuries in the crash. Four other passengers were hospitalized with non-life-threatening injuries.

Another 28 people refused medical attention, Chicago Fire Department Chief Juan Hernandez said.

“Everybody was so shook up that you don’t know what to do. You don’t know if you want to scream. Only thing you could do was look around,” Sanders said.

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According to a statement from Burlington Trailways, the global positioning system on the bus showed it was traveling at 49 mph at the time of the crash – below the posted speed limit of 55.

“Because of the damage to the bus, it will be towed to a secure facility where investigators will inspect the vehicle,” the company said.

The 53-year-old bus driver also will undergo routine drug testing, according to the company.

“In the coming days and weeks, Burlington Trailways will review the circumstances of the accident to see if there are any areas our company can improve its safety culture,” the company said.

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Police said the crash was under investigation.