On the I-15 Express Lanes in San Diego, solo drivers must have a transponder properly mounted 24 hours a day, seven days a week. Solo drivers should not enter the Express Lanes when “HOV Only” is displayed. Carpools with two or more occupants, vanpools, Clean Air Vehicles, motorcycles and transit vehicles drive for free without a transponder. No transponder is needed for qualifying carpools at this time. If qualifying carpools have a switchable transponder (FasTrak Flex), it should indicate that there are two or more occupants in the vehicle to avoid being charged a toll. Solo drivers using standard and sticker transponders are charged the full toll. Tolling agencies offer Mylar® bags for qualifying carpools to place standard transponders in to prevent them from being read and charged a toll when there are two or more people in the vehicle. Sticker transponders cannot be removed from windshields once they are adhered, so removing them to avoid paying a toll is not possible.