You are underestimating the impact of sleep deprivation, and the ability for a person to recognize the impacts while sleep deprived.
https://bmcpublichealth.biomedcentral.com/articles/10.1186/s...
"It was concluded that sleep deprivation has a greater impact on driving performance than a BrAC of 22 μg/100mls of breath, as measured by driving simulation. Coffee is not an effective countermeasure for sleep deprived driving and drivers’ ability to judge this impairment is suggested to be limited."