The unused money accounts for roughly half of the $4.5 billion the T has set aside since fiscal 2010 for its so-called capital budget.
The MBTA has been blaming its winter woes on a lack of funding. None of the lost federal money was designated for maintenance or repair, according to the Federal Transit Administration.
“However, in the past 10 years, $10.4 million in federal funding for earmarked expansion projects that were directed to MBTA have lapsed and are no longer available to the transit agency,” the FTA said, directing questions about the specific use of the funds to the MBTA.