T fare special cases

This came out of a question I answered on mbta. Let's say you're trying to get from the Museum of Science to Medford Square in the new fare regime; your plausible choices include taking the T to Davis or Sullivan and then a bus, two busses from Lechmere, or commuter rail to Malden or West Medford and a bus. It turns out that for a bus-plus-subway trip, the cheaper fares and free transfer together make not using a CharlieCard cost twice as much!

Route	Cash fare		CharlieTicket fare		CharlieCard fare
87/88 bus Lechmere to Davis, then 94/96 bus	$1.50 bus + $1.50 bus	$3.00	$1.50 bus, free transfer	$1.50	$1.25 bus, free transfer	$1.25
Subway to Davis, then 94/96 bus	$2 subway + $1.50 bus	$3.50	$2 subway + $1.50 bus	$3.50	$1.70 subway, free transfer	$1.70
Commuter rail to West Medford, then 95 bus	$1.70 zone 1A CR + $1.50 bus	$3.20	Stored-value cards not accepted on commuter rail

...but remember, the new system has fewer special cases, so it's simpler!

Route	Current fare	CharlieTicket fare	CharlieCard fare
Davis to Kendall	$1.25	$2.00	$1.70
Davis to Braintree	$2.50	$2.00	$1.70
Chestnut Hill to Reservoir	$3.00	$2.00	$1.70
Reservoir to Chestnut Hill	Free	$2.00	$1.70
Chestnut Hill to Braintree	$4.25	$2.00	$1.70

See? The new system is perfectly simple. Just so long as you don't think about how you're paying. Or transfers. I think "not thinking of any of the corner cases even a little" is the current bane of my existence.