Which type of marked utilities signifies extreme caution must be exercised due to high-voltage lines?

The correct answer is based on the standardized color codes for marking underground utilities. Red is specifically used to indicate high-voltage electrical lines. It is imperative that operators and workers exercise extreme caution when working near utilities marked in red to prevent serious accidents or injuries, as these lines carry a significant risk of electric shock and other dangers if disturbed.

Understanding utility markings is crucial for safety on job sites. Each color corresponds to a specific type of utility, which helps in identifying the hazards present. For instance, while yellow marks indicate gas, oil, steam, or other hazardous materials, and blue is reserved for potable water, these colors do not signify the same level of immediate danger as red. Consequently, construction and excavation workers must remain particularly vigilant around red markings to ensure a safe working environment.