June 1, 2008 Part of Green line closed for MBTA test Play video

(Stephen Iandoli, NECN: Newton, MA) - Sunday afternoon, federal investigators will recreate last week's MBTA crash to find out what the operator saw before the collision.

The NTSB on Saturday tested the signal and now believe speed may have been a factor.

Investigators say the trolley was going nearly 30 miles faster than it should have been going when it rear-ended the first train.

Now they want to know why.

That means Green line passengers will be bussed around the accident site.

NECN's Stephen Iandoli has more on the story from Waban T-station in Newton, MA