A full time rider pays a monthly fare and is guaranteed a seat in that particular van, regardless of how often they ride. A part time, or alternate rider would pay a daily rate just for those days they actually ride, but would not necessarily be guaranteed a ride every day. They would meet the van at their designated pick up point, and if they had available seating, the rider could commute that day, but if all full time seats are taken, the alternate rider would need to find their way in. You may check with a coordinator ahead of time to see how often they commute with a full van, and how often they have an open seat. They are typically able to give you a good guess, but again, as an alternate rider, there is no guarantee.