A morning bus ride turned into a nightmare for 29 passengers Tuesday when a coach rear-ended a tractor-trailer on Interstate 95, pinning the bus driver inside the vehicle, sending 15 people to the hospital and wreaking havoc on the morning commute.

None of the injuries were life threatening, police said.

The accident occurred just after 8 a.m., near exit 3 on I-95 south when the bus slammed into the back of a tractor-trailer, blocking the center and left lanes of the highway.

The accident prompted emergency officials to declare a "mass casualty incident" as police, EMS and firefighters performed on-site treatment to the injured passengers. The accident caused extensive delays during the morning commute with a 12-mile backup on I-95 south and congestion from Rye, N.Y., to Greenwich on the northbound side, according to the state Department of Transportation.

Eight people were taken to Greenwich Hospital and seven were taken to Stamford Hospital following the crash, officials said. Patients taken to Greenwich Hospital were treated and released as of Tuesday afternoon, officials said. All but one patient was released from Stamford Hospital as of Tuesday night. It was not clear whether the admitted patient was the driver, who suffered the most serious injuries, although they were not believed to be life threatening, according to medical officials.

State police did not release the name of the driver or the bus company.

Deputy Fire Chief Thomas Nixon said firefighters spent 30 minutes extricating the driver using the Jaws of Life and power saws.

"When we got to the scene, the bus was still running," said Nixon. "We were able to shut off the bus using the emergency switch. The front end was crushed and the driver was pinned between the first row of seats and the steering column and dashboard." Nixon said the driver remained "conscious and alert" while firefighters cut into the bus to free him.