assuming those numbers hold when scaled up, you are compressing the actual distribution into a single number (an average). Overall that high-level number may be

assuming those numbers hold when scaled up, you are compressing the actual distribution into a single number (an average). Overall that high-level number may be correct. But at the same time, the kinds of people that get into accidents will be a different distribution. How you drive factors a lot into how likely you are into getting in an accident, even allowing for the other drivers. If the distribution becomes essentially random then you might actually have a higher chance of getting into an accident than before, if you were a very careful driver. (Obviously those that benefit the most are the bad drivers since they'll no longer be bad) Just remember that whenever you summarize a distribution into a single number like an average, you loose a lot of information in the process.