Any wheelchair and its occupant must be securely restrained.
There are many systems available though most are a variation on a four-point webbing system.
There are a number of “backrest” or “rear-locking” systems, however due to their size do not suit most minibus applications.
Not all restraints are suitable for all designs of wheelchair, and some will not suit all wheelchair positions in different vehicles.
The wheelchair occupant must wear a restraint (unless travelling on a local service bus where standees are permitted). A lap belt or harness attached to the wheelchair only will not be suitable. There are several designs of restraint and all are attached directly or indirectly to the vehicle. Ideally, any restraint should pass over the passenger’s lap and at least one shoulder. A restraint with an additional high level mounting might be more comfortable for the wearer.