We are considering purchasing "greener" vehicles. Hybrid vehicles, specifically the Toyota Prius was recommended for our passenger vehicles. However, I'm pulling for biodiesel, as I think it is more economical and available for heavy-duty vehicles as well.

Is a hybrid available for heavy-duty vehicles? Is it truly an effective "fuel"?

Of course, hybrid is not a kind of "fuel"    It is rather a term which describes a system that utilizes both combustion and electric power. I could be wrong (believe me it has happened before!) but I seem to think that there are some hybrid SUV's on the market. As for heavier vehicles, I doubt you will find anything utilizing that system. Perhaps the company would consider trying both?