From the Miami Herald column immediately linked by Mr. Smith:
Fast trains are fun to ride, and much easier on the environment than the family SUV. But in the long term, people won’t keep buying tickets if it’s not cheaper, faster and more convenient than driving their own cars.
Cheaper, now how you measure that?
I could tell you my current auto is almost a year old, and its fully allocated cost at this time is $1.771/mi. That figure includes fuel, an allowance for maintenance ($.24/mi), economic depreciation (8 years), registration, insurance, subscriptions (XM and Enform), and interest (real and/or imputed). This is a different "kettle of fish" than Tax cost, and is definitely different than a teen aged kid's idea of cost, i.e. gas.
Of course, for families keeping their books on "cookie jar" accounting, I suppose tolls, parking, and "if it needs an oil chamge" would be added to fuel.
While Florida tolls are high, there is always US27 roundly following the SAL, or 95 and back roads to it. It's not like in the Corridor, where tolls (and Amtrak fares) are "killers" and are unavoidable.
So "cheaper" is in the mind of the beholder.