People often view their 18th birthdays as one of their first rites of passage: buying a lottery ticket, registering to vote -- paying $2 to ride a bus?

If you didn't spend the summer bumming around on the couch or soaking up the sun in distant lands, you probably already noticed that Muni fares increased on July 1. But whether transit riders have been fishing in their pockets for that extra change for the last couple of months or for the last couple of days, many are wondering: Wasn't there supposed to be a student rate for ages 18-24?

Instead, on the eve of your 18th birthday, you'll pay 75 cents to hop on a bus. The next day, you'll be forking over an additional $1.25. Instead of celebrating, you now cannot afford that large cup of coffee at Cafe Rosso.

At a time when the San Francisco Municipal Transportation Agency is strapped for cash -- so is everyone else. But with little enforcement, many riders sneak on buses through the back door, hastily wave expired transfers in drivers' faces or even dare pretend they're still a minor to pay the discount fare.

A large portion of Muni ridership falls into the 18-24 range -- the same age group that faces high unemployment or is often still scraping by on minimum wage.

Metropolitan Transportation Commission findings from 2007 showed that those who could least afford to ride public transit were also among the most dependent on it. Of riders ages 18-24, 27 percent were public transportation dependent and 34 percent of the respondents reported a gross household income of less than $15,000.

Things are going to get a little tougher still, come Jan. 1. The cost of an adult monthly fast pass will rise $5 from $55 to $60 -- and will no longer include BART access. For a premium Muni/BART pass, prepare to pay $65 each month.

Riding a bus might mean the difference between grabbing a quick bite before class or grumbling through it. Everyone's wallets -- and stomachs -- could really use a break.