In METAR reports, what does the prefix "R" before a runway number indicate?

The prefix "R" before a runway number in METAR reports indicates runway conditions. This code is used to provide information about the surface conditions of a specific runway, allowing pilots to assess whether the runway is suitable for takeoff or landing based on factors such as wetness, snow, ice, or other obstructions. The use of this prefix is essential for safety and operational efficiency in aviation, as it directly influences the decisions pilots make regarding runway selection and approach.

The other options, while relevant to runway information, do not accurately describe the meaning of the "R" prefix. For instance, runway length and width, orientation, and traffic levels are important considerations in aviation but are conveyed through different means or terminologies in METARs and not specifically indicated by the "R" designation.