I'd love it if you could provide a sources and uses chart. In general, according to Brookings, drivers tolls, excise, tag fees, and gas taxes only amount to 60% of road budgets--the rest comes from property taxes and general revenues (the cities and towns rely heavily on property tax, for example).
Sure. Here goes:
MBTA Operating Expense = $1.57B per year.
MBTA Debt Service = $0.45B per year.
http://www.mbta.com/uploadedfiles/About_the_T/Financials/FY16PreliminaryBudget31115.pdf
MBTA Capital Expense = $0.4B per year from the State, another ~$0.1B from the Feds for GLX = $0.5B per year.
https://www.massdot.state.ma.us/Portals/0/docs/infoCenter/docs_materials/CIP_FY16.pdf
Total MBTA Expense = $2.5B per year or so.
Total Riders in 2014 = 1.3 million
http://www.mbta.com/uploadedfiles/documents/2014 BLUEBOOK 14th Edition.pdf
Total MBTA expense per rider = $1,923
Cost of 12 link passes beginning in July: $1,014
Excluding sales tax, each T rider gets a subsidy of $900 or so per year.
_______________________________________
Now, let's look at drivers. This is calculated differently.
Total annual budget for MassDOT Highway Division (including operations) = $1.65B
https://www.massdot.state.ma.us/Portals/0/docs/infoCenter/docs_materials/CIP_FY16.pdf
Total annual gas tax revenue for MA (paid only by drivers) = $0.237B
http://www.taxpolicycenter.org/taxfacts/displayafact.cfm?Docid=401
Total annual toll revenue for MA (paid only by drivers) = $0.2B
Total Chapter 90 funds for municipal road projects (the Commonwealth basically pays for municipal road projects in most places, not property tax) = $0.2B. To account for the cities and towns that do self-fund roads, let's double it. = $0.4B.
Total revenue from fees and sales (i.e., Motor Vehicle Registration, Fines, etc.) = I don't know, but I know NH makes $0.115M per year on them and is 25% the size of MA, so I'm going to say $0.45M
So, the net annual subsidized cost of facilities for cars in MA is:
$1.65 - $0.237 - $0.2 - $0.45 + $0.4 = $1.163B per year
Number of MA registered vehicles = 3.86M
http://www.slideshare.net/ibmelanie/mass37-melanie2
So, subsidy to drivers = $300 per year.
Total cost to own a car in MA = $2,169
http://www.bankrate.com/finance/auto/car-ownership-costs-by-state.aspx
_______________________________________
$900 for T riders (or 90% of their annual cost), $300 for drivers (or 15% of their annual cost).
Now, we aren't counting outside taxes, but there are more non-T riders paying sales tax (and the taxes that support the annual top-up funding the MBTA receives from the General Fund) than there are non-drivers paying the taxes that support Chapter 90 and municipal spending.
You can say I left out "externalities", but you'd be arguing that the externalities of driving are twice the size of the base subsidy at $600 per year per driver. That's pretty steep.