A 77-year-old Framingham woman was struck and seriously injured Friday by an MBTA commuter rail train in downtown Framingham. The woman was struck by an inbound train traveling on Track 2 near the Framingham commuter rail station around 7:20 a.m., said Framingham and Transit Police. She was hit near the intersection of Routes 135 and 126, an MBTA spokeswoman said, and the incident led to the temporary closure of a main intersection and delays for commuters. The woman was taken by MedFlight helicopter to a Boston hospital, where she was being treated for serious injuries, Transit Police said. At the hospital, the woman spoke briefly with police, and the circumstances of the incident remained under investigation, Transit Police said.