When the "Mighty Mac" was first built there was a perpetual trust fund set up to pay for maintenace costs etc. This trust was later raided by administrations bent on off-setting deficits to the state's general fund. The latest effort was tried by the out going Gov. who wanted the fund to offset job losses in the auto industry and decreased funds etc from the economic disaster of 2008. I think her efforts were mostly thwarted but it could be part of the reason tolls keep rising, mismanagement by administrations who were sworn to protect it.