The most common and most likely answer to this crossword clue is the 3 letter word AAA
A
A
A
Buddy explains!

The straight part
We know that "US drivers’ club/top credit rating" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case us drivers’ club/top credit rating = aaa.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does AAA mean?
AAA noun- Initialism of abdominal aortic aneurism.
- Initialism of acquired aplastic anemia.
- Initialism of acute anxiety attack.
- Initialism of androgenic anabolic agent.
- Initialism of anti-aircraft artillery.
- An alloy containing mercury.
- A combination of different things.
- One of the ingredients in an alloy.