Federal rules require a commercial driver's license for a vehicle designed to carry 16 or more people including the driver, or one with a GVWR of 26,001 lbs or more. A bus built for 14 passengers plus the driver, under that weight, falls below both lines, so a church, senior living community or business can hand the keys to any licensed staff member.
Every bus and van on this page seats 14 passengers or fewer, new and pre-owned, with or without a wheelchair lift. Ask a rep to confirm the GVWR of any bus you're considering, and check your state's rules for your use: some states and programs, child care especially, add requirements of their own.