Which of the following is NOT a type of railway switch?

The correct choice highlights the absence of a "Digital switch" as a type of railway switch. Traditional railway switches are designed to guide trains from one track to another and can be operated through several means, including mechanical, electric, and manual methods.

Mechanical switches rely on physical mechanisms to change track alignments, such as levers or rods. Electric switches utilize electrical power to automate the switching process, making them more efficient in busy rail operations. Manual switches, on the other hand, are operated by personnel, requiring physical intervention to move the switch.

In contrast, a "Digital switch" does not represent a recognized or standard classification of railway switching mechanisms. While modern technology may integrate digital controls into railway systems, this term does not refer to a specific type of switch that is routinely used in rail operations. Thus, "Digital switch" stands out as the option that does not belong among the established types of railway switches.