Recent studies suggest that road signs have an automatic priming function in addition to conscious transmission of information. The current study investigated the priming effects of traffic signs, and how they are influenced by stimulus location and duration. An initial experiment investigated the repetitive and semantic priming effects and their relation with stimulus type (symbol, word, or both). A second experiment varied the location of the stimuli across stimulus type (left, middle, right) and a third experiment varied stimulus duration. Strong repetitive priming effects and weaker semantic priming effects were found. The results indicated that while semantic priming caused slower reactions compared to the repetitive priming, written signs in the semantic condition and symbolic signs in the control condition created the shortest reaction times. Moreover, the best reaction times were obtained when the traffic sign contained both word + symbol. It was also found that speed hindered drivers' responses and weakened the priming effect of the traffic signs. In conclusion, the overall results are significant in showing that the effect of the semantic priming is reinforced when the signs containing word + symbol are presented for longer durations; hence, the more frequent use of written road signs and the decrease in velocity provide a stronger priming effect and shorter reaction times, which may result in less collision and traffic accidents. (C) 2007 Elsevier Ltd. All rights reserved.