Trainz

Is the American standard gauge the largest (widest) gauge in the world for rail transportation? How big can trains and train tracks get in size, mass and scale before they just become not feasible? This question can also be asked about other vehicles, aircraft and vessels. Is a jet airplane literally one mile long just plain impractical? How long does the wheelbase of an automobile get before it loses all feasibility? How large does even a seas ship have to get to where it simply just doesn't cut it?