Even unintended actions can be unjust. Let us take your example of the drunk driver causing injury or death. Although the accident was unintended, it is still unjust because the person knew that he or she would be driving. Starting to drink that evening was not wise. Surely, before the person became drunk, he or she had the rational faculties to know that the amount of alcohol consumption was not good. So, prior bad judgements before the accident show that the unintended consequences had bad choices connected with it. Those choices were unjust choices and so those injured or those who lost loved ones can forgive if they so choose.