Carpooling rates have fallen in recent years from 13.4 percent of commuters in 1990 to 10.7 percent in 2005, according to the Federal Highway Administration. Most of the rides posted on Carpool so far are in California, but there are also rides offered around the country, and even a few in England.
Transportation commentator Robert Puentes thinks the idea will continue to spread. "I have no doubt there is a tremendous demand for an application like this," said Puentes, a Brookings Institution fellow and affiliated professor at Georgetown's Public Policy Institute. "The younger generations are poised to take a different approach to transportation."
Puentes says it's more expensive than ever to own a car, which can account for about 20 percent of a household's annual budget on average. Add in concerns about global warming and it's a potent combination. "The green movement — it's a real thing and it is affecting decisions," he said.
Robin Chase is banking on it. She founded the Facebook ride-sharing service GoLoco this year, but she's not new to the game. In 2000, she leveraged Internet and wireless technology to create Zipcar, a car-sharing company that lets urbanites rent vehicles for short periods, even by the hour. The company now has more than 100,000 regular customers.
GoLoco has a few differences from Carpool — the main one being that users can complete the financial portion of a ride-share deal online, with the site taking a 10 percent cut of the transaction. Chase says handling money online can bypass the awkwardness of doing it in person; for people who ride together a lot, it can help keep track of who owes what.
Chase is passionate about the environmental side to GoLoco, which she says is meant to conjure up "going local, low cost and low CO2."
"Personal cars are 20 percent of CO2 emissions, and the absolute No. 1 easiest thing to do to reduce our own personal carbon footprint is to share car rides or to reduce our miles traveled," she said. "Starting tomorrow, you can make a dent."
While some carpoolers cite money and others the environment, there's another key factor that is, after all, what Facebook is all about: social connections.
Lauren Fisch, 24, used the Carpool application to find someone to share her commute to Silicon Valley. "It can take more than 90 minutes some days, so it's really nice to have someone to talk to," she said.
"A car pool can be a real pain, unless there's an added value for me and for everyone else in the car," she said. "I care about having company and I care about being green."
Sacramento State's Najm said, "It's half and half between a social and convenience thing. … I've met tons of people and some of them I've actually become real friends with."
Still, it's not for everyone. Dayana Perez, 22, who lives in New York City, says she wouldn't ride with a person just because they were Facebook friends. "That could be someone you met at a party two years ago. It's got to be someone who's a real friend for me to drive with them."
Beyond the natural audience of college students, it's anybody's guess whether ride-sharing will catch on with a wider group. Older people are joining Facebook in droves, with people older than 35 now making up more than one-third of members.
Puentes says the biggest challenge for these programs is the same one that faces carpooling in general: As cities become more spread out, it gets harder to match riders to destinations, because fewer people are heading to and from the center (if there even is a real center anymore).
But he remains optimistic. "Things that were dismissed in the past are looking much more positive," he said. "It's a market that shouldn't just be a niche market. We're just on the cusp, I think, of more dramatic changes."