Uber announced today that it was expanding its carpool service to the East Bay cities of Oakland, Berkeley, and Alameda, in a bid to appeal to residents who want to use the ride-hail service to commute to work in San Francisco. UberPool, in which riders pay a cheaper fare to share a car, now makes up nearly half of the company's trips in San Francisco. "It's all about getting more butts into fewer cars," Wayne Ting, Uber's general manager in San Francisco, wrote in a blog post.

UberPool is also another way for the company to tout its commitment to improving the environment. Uber claims that one month of carpooling in San Francisco "saved 120 tons of carbon dioxide emissions when compared with non-pooled trips, the equivalent to the output of over 128,000 pounds of coal." Previously, Uber announced fixed-rate rides between SF and Silicon Valley in the hopes of appealing to commuters who weren't inclined to use public transportation like buses or the BART train.

"It's all about getting more butts into fewer cars."

Not all drivers are as enthusiastic about UberPool as the ride-share company, though. Many have told me that customers may like the cheaper fares, but they are often annoyed when a pool ride takes them out of their way to pick up additional passengers, and that can negatively affect a driver's rating. Also, some drivers say pool rides aren't worth it for them financially: if a rider selects a pooled ride but the driver can't find another passenger, the original rider still pays the discounted fare, meaning less money in the drivers pocket.

Since launching in San Francisco in 2014, UberPool has expanded to around 15 cities, including most major US, European, and Chinese cities.