Structural considerations in building locomotives ranged from the finest detail to the largest feature. American railroad tracks were made of light iron and wood with more curves and inclines than their British counterparts so designs were revised to improve traction and maneuverability. The main goal was to get maximum power to the wheels, driving the locomotive at the highest speed and avoiding derailment and excessive track wear or damage. The risk of explosion and fire also had to be taken into account.
Such varied conditions precluded standardization!