The potential growth of railway traffic is expected to be substantial worldwide; hence, railway companies and agencies are looking for better tools to allocate their capital investments to capacity planning in the best possible way. This paper presents a comprehensive decision support framework with three stand-alone tools for strategic railway capacity planning: (1) “Alternatives Generator,” which enumerates the possible expansion options along with their cost and capacity effects; (2) “Investment Selection Model,” which determines the portions of the network that need to be upgraded with certain capacity improvement alternatives; and (3) “Impact Analysis Module,” which evaluates the trade-off between capital investment and delay cost. This research also developed and implemented a specific decision support framework for North American class 1 railroads. On the basis of the network characteristics, estimated future demand, and available budget, this decision support framework can successfully determine the optimal investment plan. This tool can significantly help railroads maximize the return on investment from capacity expansion projects, thus enhancing their ability to provide reliable service to customers.