Casual carpool is an alternative method for creating carpools. It emerged in the 1970s in San Francisco and Washington DC and has steadily grown since, also appearing later in Houston. It's valuable to thousands of commuters as it provides an unparalleled convenience and amount of time savings. It's different from a traditional scheduled carpool because of its ad-hoc nature.
Casual carpools are formed between at least two riders and one driver at the pickup locations in the East Bay during carpool lane hours (5:00am-10:00am). Because both riders and drivers can form a carpool almost immediately when they arrive, it can be faster than relying on a traditional carpool and is almost always faster than driving individually or taking BART.