Tahoe Area Regional Transit (thank you, H.!) is the most easily found example of TART in transit, however, Traverse City has a trail network called TART (Traverse City Area Recreation and Transportation Trails according to http://www.traversetrails.org/about/faq/
I wish there were more, however.
Here's some history about the FART (Fairfield Area Rapid Transit).http://www.dailyrepublic.com/featured-stories/new-community-column-kicks-off-with-memories-of-famed-fart/
And a modern version for hire:http://www.shortbusrides.com/
Foothill Area Rapid Transit, a "Premier Limo Bus Service"
And from Italy, where FART doesn't mean what it means here:
Ferrovie Autolinee Regionali Ticinesi (FART)http://wikitravel.org/en/Rail_travel_in_Europe
People do use CART, MART, etc.