Police said the truck driver apparently was reversing out of a construction site and collided with the passing tram.
The sun rose Thursday over a somber ceremony marking the third anniversary of the deadliest mass shooting in modern U.S. history.
Five people were hospitalized in critical condition — including two police officers who were the first at the scene — but their lives are not in danger.
The van overturned and its roof collided with the front of the larger bus.
At least 10 students were on the bus and six of them were taken to hospitals with non-life-threatening injuries.
A natural gas explosion killed two people, injured seven, and destroyed three row houses.
No gas odors were reported prior to this morning’s event and BGE did not receive any recent gas odor calls from the block of homes that were damaged.
Police said at least three shooters may have been involved, though no arrests were immediately announced.
A fourth house in the row was partly destroyed, and the neighborhood was strewn with glass from shattered windows.
U.S. officials said the administration also plans to provide at least $15 million in disaster assistance.