We live by laws, not by abstractions.
We live by abstractions. That's why we're allowed to have Common Law as well as have judges interpret laws. Laws in and of themselves are concrete and insoluable. The interpretation and application of them are less so. The law he broke was being in the intersection when the light turned red. Following the law he would then be fined. However the purpose of the law is to act as a gauge for what is allowable in society.
Breaking the law is a "crime" if you take it at face value but the purpose of the law behind stopping at red lights is to prevent accidents. Had he stayed he would have likely caused one. In this case staying with the law would cause damages that the law was designed to prevent.
It is arbitrariness in the enforcement of laws which may be unjust.
Yes, it is.