Railroads are increasingly using new technologies to improve capacity and operating efficiency. To plan their investments and prepare for the implementation of these technologies, railroads must understand their net effect on operations. This requires understanding both the particular aspects of these technologies that affect capacity and the characteristics of the systems into which they are being introduced. Two important technologies in this regard are communications-based train control (CBTC) and electronically controlled pneumatic (ECP) brakes. Each element of CBTC and ECP brakes with the potential to affect capacity was identified, and its effect under various implementation scenarios was evaluated. The potential impact of each element was assessed and compared with the various baseline conditions and conventional technologies to understand the incremental effect. An extensive review of the literature on the subject was conducted in support of these evaluations. CBTC implementation with enforcement braking will generally result in a loss of capacity, but as these systems become more fully integrated, the potential for capacity enhancement improves. ECP brakes will provide benefits under most operational scenarios because of the shorter braking distances and thus the potential for the closer spacing of trains. The two technologies have a potential interactive effect: CBTC may make it possible to more effectively take advantage of one of the principal benefits of ECP brakes: shorter stopping distances. The results for either technology will be route and network specific, so individual railroads will need to conduct analyses to understand the net effect on the capacity of their systems.