The former, obviously. However, according to this Bank of America ad, it's just dandy to preface "Muni" with a definite article. Wanna fight about it? Fine. Head over to Muni Diaries or Language Log where heated linguistic debates are in progress.

Bait alert: We should point out that, of course, using "the" in front freeway numbers, so says your righteous SoCal-born editor, is not only acceptable but encouraged.

[Muni Diaries] [Lang Log]