I removed this from one of the posts regarding the Halloween storm for two reasons; I didn't want to hijack the original thread, and I wanted to flesh out things more.
Route 21 is a good route for those who use the Orange and Red lines and don't want to loop through downtown. On the off-peak and the weekends, Route 21 does run consistently (albeit infrequently; on Saturdays it's every 40 minutes and Sundays it"s every hour). Read more.