Rail car modularized modification programs altering the nature of the center sill in the modified railcar and the modified railcars formed thereby

A method of modification of a railcar to form a modified railcar comprising the steps of:

• Providing an existing donor railcar with a pair of truck assemblies and a center sill design of one of i) a stub sill and ii) a through sill;
• Removing an upper portion of the existing donor railcar;
• Forming an underframe construction configured to be above the truck assemblies and having a center sill design of one of i) a stub sill ii) a through sill, and iii) a fish-belly center sill, wherein the underframe construction has a center sill design of one of a through sill and a fish-belly center sill when the center sill design of the existing donor railcar is a stub sill, and wherein the underframe construction has a center sill design of one of a stub sill and a fish-belly center sill when the center sill design of the existing donor railcar is a through sill;
• Forming an upper body of the modified railcar;
• and
• Attaching the upper body of the modified railcar to the underframe construction.