Three or more, unless you ride a motorcycle, in which case you can use the lanes without paying a toll. But again, you’ve got to have a FasTrak Flex tag on you, otherwise the overhead cameras ...
Richmond-San Rafael and San Mateo-Hayward — vehicles with two occupants will be allowed to use the carpool lanes if they are equipped with a FasTrak Flex toll tag set to the “2” position.
Solo drivers who want to use the express lane must have a standard FasTrak or a FasTrak Flex toll tag, while carpoolers and motorcycles must have the FasTrak Flex toll tag to travel at a discount.