On December 5, 1921 a head-on collision occurred on a single line of track near Bryn Athyn station. The collision resulted in a fire and ultimately claimed 27 lives while injuring 70 others.

The railway was a single track coordinated by time-tables and train orders. Before leaving the station, the engineers would be given written orders in regards to the expected rail traffic. The first train, No. 151, was a locomotive, a combine car, and two passenger cars. It had departed from Philadelphia traveling northeast. On this same route was Engine No. 154, a milk train, running late. Engine 151 had pulled into a siding to allow No. 154 to pass. The engineer had been given written orders to wait for No. 154, but to also wait for Engine No. 156, another passenger that would be traveling this railway. However, the conductor of Engine 151 overlooked these orders and proceeded after No .154 had passed, despite the block signal being down, meaning the train was supposed to remain stopped.