I work with an adult male with special needs who gets out of his seat belt in the van and starts walking around the back seat.
I think the first thing to consider is why he wants to move around the van. For example; is the desire to move around related to any specific positioning or support needs which are perhaps not being addressed? Are there any health concerns which require specific monitoring (e.g. high-functioning autism, low-functioning autism, ADHD, etc.)?
Equally, as you mention ‘work’, are there any parameters regarding insurance or financial budgets that need to be considered? Is the vehicle in question a school bus type van or minivan style of vehicle?
Are there any 5 point harness boosters that would fit him or do you know of a speicalized chair he could use?
I certainly don’t have the knowledge of experienced CPSTs here on the forum, but I believe that using a product designed specifically for use with a standard vehicle seat (e.g. a seat, harness or vest) is considered the preferred option over a securing a transport chair or wheelchair. However there are definitely options available with regard to both scenarios.