What were the technological innovations that allowed for the rapid expansion of the railroads?

There are different phases of railroad expansion with the innovations in technology.

Explanation:

Few of the technological innovations are described below that leads in railroad expansion more rapid.

1. Centralized Traffic control (CTC) is introduced in 1960's that is used to control the traffic on railroads using different signal control.

2. In 1990's after computer technology involvement, railway ticket and reservation system is automate and being centralized. That makes the railroad expansion improve.

3. Bullet train technology has been introduced, that makes the railway trains more faster.

4. Electric trains has been introduced to use green energy and reduce the dependency on the fuel to make environment clean and green.