The correct answer to the question, "The friction factor used in geometric design of highways is provided by the:" is the "Indian Road Congress (IRC)".

Here is a detailed explanation of why IRC is the correct answer:

1. Role of Indian Road Congress (IRC): The IRC is the apex body of highway engineers in India, providing standards and guidelines for highway engineering, construction, and maintenance. It emphasizes safety, functionality, and efficiency in road design, including the friction factor, which is crucial for ensuring vehicle safety and performance on road surfaces.
2. Importance of Friction Factor: In highway engineering, the friction factor is critical for determining the interaction between vehicle tires and road surfaces, impacting aspects like braking distance and skid resistance. Proper friction consideration is necessary to design safe and efficient roadways.
3. Exclusion of Other Options:
   • Bureau of Indian Standards (BIS): While BIS sets comprehensive standards across various sectors, its focus is not specifically on the detailed design aspects of highways such as the friction factor.
   • Ministry of Railways: This ministry primarily oversees the railway network in India and does not engage in highway geometric design.
   • National Highways Authority: The National Highways Authority of India (NHAI) is responsible for the development, maintenance, and management of national highways but follows the standards set by the IRC.

These points illustrate why Indian Road Congress (IRC) is the authoritative body providing friction factors used in geometric design of highways in India.