Being a big fat person, I'm struggling to predict what would happen if I were to do this.

From my experience going down hills on my bicycle, I can predict that I would get going a lot faster due to having more mass for gravity to act on. But would it be enough to launch me far enough upwards again at the end? I don't generally have to pedal very hard to get up the hill at the other side of a train underpass, for instance, because I usually get a lot of speed going downhill.

I think my increased surface area would work against me here where it doesn't on a bicycle (tires are the same thickness no matter how big you are) and cause more friction that would work against gravity, and I'd probably end up sort of plopping off the end of the ramp into the dirt