 Federal safety officials have started an investigation into a Chicago commuter train crash that left almost 40 people injured. Jennifer Homendy, chairperson of the National Transportation Safety Board, said during a news conference Friday that a team of seven investigators from her agency have started documenting the scene of the crash. She said they have not reviewed event recorders or video of the incident yet. Investigators expect to spend about five days on scene with a preliminary report expected in a matter of weeks. The train rear ended snow removal equipment traveling ahead of it on the same tracks Thursday. We have not yet reviewed the event recorders or the inward and outward facing cameras. We will do that shortly right now. Today was about collecting what we could and documenting the scene. We always ask for on who was around the track, what was around the track. That's documentation we always ask for as part of the investigation. In addition to that, we will start scheduling witness interviews including employee interviews and company interviews and that will help determine what was going on.