Carli Velocci photographed the bus that is now preventing outbound B Line trolleys from moving in Allston.

How the bus wound up there is under investigation by Veolia Transportation, which runs BPS buses, a BPS spokesman said.

We believe there were five students on board when it happened. Everyone is fine and another school bus already came to pick them up and take them home.

Michael Tousley shows us another view of the blockage: