The 90 class were designed specifically for heavy coal haulage in the Lower Hunter Valley region of New South Wales, to meet the required specifications the class was designed with much heavier frames than typical for locomotives then in use specifically to increase their tractive effort.
The 90 class locomotives were designed to handle the heavy coal transportation needs in the Lower Hunter Valley region of New South Wales by incorporating heavier frames than usual for locomotives at that time, thereby increasing their ability to exert traction power.