A Greyhound bus was recently involved in a fatal accident with a tractor-trailer as passengers made their way from NYC to Cleveland. The accident happened as the bus passed through central Pennsylvania. Most people on board were taken to local hospitals with injuries; one person died.

According to CBS New York, the accident happened at about 1:45 a.m. in the westbound lanes of I-80. The bus allegedly ran into the rear of the tractor-trailer as it was hauling bales of garbage. The impact crushed the front of the bus.

Forty-five of the 50 people on board the bus were taken to area hospitals. One woman was killed, and four were listed in critical condition.

The driver had been working with Greyhound for more than 12 years, according to a spokesperson for the company. They are conducting an internal investigation as authorities conduct their own into what caused the accident.

It isn’t clear what caused the bus driver to plow into the rear of the truck. Potential causes include   distracted or drowsy driving, which are leading causes of serious accidents.

The driver of the semi-truck described to the local news how he assisted in pulling people out of the bus after the collision. He helped passengers crawl out of the windows. One passenger, he said, was trapped by his trailer, which had struck the side of the bus and pinned a man in his seat.

The moments leading up to the crash were likely quiet. Because of the time, many people were probably asleep, not knowing their lives were about to be turned upside down.

While buses are designed with passenger safety in mind, the accidents they are involved in frequently happen on highways when the vehicles are traveling at a high rate of speed and the risk of serious collisions is greater.