You can get a class C cdl wiithout a road test. You need "general knowledge". You can add "tank" and "hazmat" for sure, and maybe "passenger" since your class D already convers a van ( but that's a grey area ). you don't need the air brake test for a class c cdl.
A long, long time ago I took all the tests in mass ( gen, airbr, pas, tank, doubles, hazmat, & como ). So I got a maxed out class A permit.
I wanted to ensure that I would keep my endorsements to so I asked them to give me class c cdl. I said "endorse my current lic"I got a cdl with hazmat, tank & passenger on my class c, but at the time it was an 11 passenger requirement. Now, I think it's a 16 passenger rule now.
Just for added info the double & triples stayed in the system for me without a class a lic for over 10 years.
Keep in mind by doing this your legal alcohol limit goes down to .04 even in your personal car (correct on the number if I'm wrong).
What it comes down to is endorsements verse licenses.
I would say that C,B,A are licenses ( as well as the passenger & school bus endorsements )
The endorsements would be hazmat, tank, doubles, air brakes ( as well as passengers & school bus endorsements )
It would seem that the passengers & school bus endorsements are kind of a hybrids ( endorsement & lic ).