arrow black black-on-white communicating communication direction directional gray grey indication law no-alternative one-way one-way-signs only pointer pointing reflective sign signs specific street-sign traffic traffic-flow traffic-sign white caution drive fire go green lights red road stop street traffic light traffic lights transport walk way ligths blue bright one way only direction pointing back traffic flow traffic sign arrows divergent diverging splitting splitting-up turn turning two-way left-turn vehicles vehicular wording danger driving pictogram road sign Road Warning Sign snow snow ahead snow sign snowing warning sign winter highway intersection interstate light street scene streets visual visual communication yield