Most states have codified it. States don't start from scratch when they set up traffic laws, fire codes, electrical codes, building codes and other ordinances. They use things like the National Electrical Code, the US Fire Administration, and other sources to use as the basis of their own codes. There is no need to re-invent the wheel on things that are basic and common to all areas of the country. Most codes were written from experience and have already withstood any legal challenges. That is why the signage at gas stations is pretty much universal no matter what state you are in.
