So a couple of weeks ago I was in San Diego, CA, for vacation; and I was looking at the trucks on the roads. The trucks in California are very different from the ones we have here in New York (well, a lot of things are different about California, but that's another story ). One of the setups that caught my attention were single drive axle tractors pulling tandem single axle belly-dump trailers. I'm not sure about the rest of the country, but I'm pretty sure that wouldn't fly here in New York. Especially driving them down city streets!
Now, about these set-ups. Are both of the trailers 28ft semi-trailers with a dolly under the second trailer; or is it one semi-trailer and the second one is a full trailer (no dolly & two axles). It's more of an academic question as scratch building something like that is way out of my league.