In Level of Service ratings, which letter denotes the worst service?

• A. A
• B. C
• C. F
• D. B

Answer: (C)

In Level of Service ratings, performance goes from best to worst using letters A through F. A is free-flow with little or no delay, and the levels degrade through B, C, D, and E as congestion increases. F marks a failure—the worst possible operation where the demand cannot be met effectively. So the correct choice is the one tied to that failure designation. The mid-range level shown in the other option is not the worst.