Various advanced train control systems are currently under development around the world, and they have been considered as the potential solutions to the substantial increase in future demand. However, the actual capacity impact from these systems is more complex and needed to be discussed. In this research, I reviewed the advanced train control systems developed in Japan, Europe, and the US, and then proposed a method to classify these advanced train control systems into six types according to their special features: ATP supervision, ATP data transmission, movement authority, ATP data format, block type. This study also developed a set of capacity equations for different types of operational scenarios and/or systems. These quantitative analyses were carried out to help railroads understand that how these technologies may enhance capacity, have little or no effect, or even reduce capacity.