It's plausible that 20% of drivers crash enough for 80% to be above average

'According to the AA Charitable Trust, 40% of UK drivers have crashed by the time they are 23 years old, and 26% of drivers have crashed within two years of obtaining their licence. (Source: https://m.toptests.co.uk/driving-statistics/)'

Although maybe not

I was a pretty crap driver before I was 23 (regardless of what I would have said then), but I'm not too bad now. Although, it depends on what you measure, I suppose; I've driven behind a Waymo vehicle, and they stay in the lines a lot more than me (which could be a positive for following rules, or a negative for increased drive times), but I also didn't ever change lanes into a bus expecting it would move, and I can avoid some of the annoying driving behaviors I used to see with Waymo (signal a lane change, decide not to do it, loop); not sure where they're at with that since I no longer live in their test areas.

thanaverage.xyz actually suggests that only 54% of people think they drive better than average, with 19014 participants

https://thanaverage.xyz/

Could you share your source?

Here is one of the classic research papers on the subject:

Iain A. McCormick, Frank H. Walkey, Dianne E. Green, Comparative perceptions of driver ability— A confirmation and expansion, Accident Analysis & Prevention, Volume 18, Issue 3, 1986, Pages 205-208, ISSN 0001-4575, https://doi.org/10.1016/0001-4575(86)90004-7. (https://www.sciencedirect.com/science/article/pii/0001457586...)

"Hi, this is a recorded interview for a study we are running, have you ever committed an illegal act?"

"Nah."

"Thanks."

Can you see the bias?

I would indeed see the bias if that was the question that they were asking. Was it?

Almost.

They were asked to answer whether they considered themselves "foolish, unpredictable, unreliable, inconsiderate, dangerous, tense, worthless and/or irresponsible". Very few people would have answered truthfully.