As far as I know, no state legislature in this country has completely given up traffic code rulemaking, so legislatively passed rules would always take primacy,

As far as I know, no state legislature in this country has completely given up traffic code rulemaking, so legislatively passed rules would always take primacy, and if you wanted that enshrined you could get it done. After all, DMVs don’t have the power to set criminal penalty standards for things like DUI, seatbelt laws, etc. And traffic cameras usually have to be enabled by state legislation since they result in penalties, so the same law could also involve minimum standards on yellow lights.