What action is indicated by the code 10-21?

The code 10-21 specifically indicates "Call by telephone." This code is part of a standardized system used for communication among transit personnel, helping to ensure clarity and efficiency within operations. When someone uses this code, they are directing that a telephone call needs to take place, typically for more detailed communication that cannot be effectively conveyed over radio or other means.

The use of 10-codes, including 10-21, helps streamline communication, making it easier for transit employees to convey precise messages quickly and reduce misunderstandings. In this context, knowing that 10-21 refers to a phone call can aid employees in responding promptly to field situations where immediate verbal communication is essential.