Updated 08/29/14 – 11:47 a.m.

CHICAGO (CBS) — Officials have reopened all lanes of the Interstate 190 entrance to O’Hare International Airport, after it was closed when a privately owned shuttle bus crashed into a concrete median. Fourteen people were taken to hospitals.

Fire Department District Chief Tim Sampey said the crash happened just before 6:30 a.m. at I-190 and Bessie Coleman Drive.

“The bus appeared to just come to a sudden stop; unknown as to why. That’s under investigation,” Sampey said.

CBS 2’s Mike Puccinelli reports all but one lane of the I-190 entrance to O’Hare reopened by about 8 a.m. The lanes were briefly closed again around 8:45 a.m. while the damaged bus was towed away, but all lanes reopened within a couple minutes.

The front of the bus was severely damaged in the crash, leaving the driver pinned inside. Sampey said it was unclear how fast the bus was going at the time.

Two firefighters happened to be behind the bus in separate vehicles, and witnessed the crash. One of the firefighters grabbed a hammer from his car and broke a window on the bus to get to the driver. The firefighter and an airport employee who arrived at the scene helped get the driver out of the bus while the other firefighter boarded the bus and began triage on the injured passengers.

The firefighters called for 10 to 12 ambulances and other fire equipment. After conducting triage, 14 people were taken to hospitals, and two others refused further treatment at the scene.

Four of the victims were triaged as “red” – meaning serious to critical condition – for precautionary reasons, but Sampey said all of the injured victims were “stable.”

“We’re not taking any chances. They had a severe crash; severe impact on the median and guardrails,” he said.

Sampey also said one of the people taken to the hospital was one of the firefighters who helped get the driver out, but it was unclear what type of injury the firefighter suffered.

The bus was a privately-owned vehicle with a sign indicating it was carrying passengers from Parking Lot E, an economy lot at the farthest reaches of the airport. The name of the bus owner and driver were not immediately available.

The I-190 entrance to O’Hare was closed while emergency crews helped all of the passengers get off the bus and conducted triage.

“Your adrenaline starts flowing, you’re excited, you’re scared. So we encouraged them to stay where they’re at. We collar and board all of them, and we take them off so as not to cause further harm to themselves,”

Dozens of people who were in cars stuck in traffic behind the crash scene got out of their vehicles and began walking to the O’Hare terminals while the lanes were closed. Sampey said the combination of the traffic backup and people walking on the shoulder to get to the airport delayed some ambulances reaching the scene, so police and fire officials helped direct people to a safe route to the airport so emergency vehicles could get through.

“People were basically bailing out of their vehicles in an effort to make it to their flights, and it’s understandable, but at some point in time we had to gain control of them to get them off the shoulders where the emergency vehicles were trying to get to the scene,” Sampey said.

Officials said the cause of the crash was under investigation.