TTC CEO Andy Byford says the collision of three streetcars this morning near Queen St. E. and River St. is “a mystery and a concern.”

Paramedics received a call around 2:30 a.m. Friday. One person sustained minor injuries when the streetcars collided and was taken to hospital.

The collision is a mystery for TTC investigators because streetcars contain three braking systems for rollback protection.

Bryford said the first in a line of three cars rolled back about 60 feet colliding with a second car, which in turn pushed back a third vehicle. Damage to the third car was minor.

“Even if the driver’s incapacitated the vehicles should not roll back like that. But it did roll back,” Bryford said.

All the vehicles were the old streetcars. None of the new Bombardier cars were involved in the collision.

The TTC is also investigating why three vehicles were in such close proximity shortly about 2:15 a.m. when traffic congestion is not an issue.

The “sandwiched” streetcars were cleared and the intersection was re-opened at 7:30 a.m.