THE ERGONOMICS OF ROAD SIGNS - EXPLICIT AND EMBEDDED SPEED LIMITS

The European traffic sign system encodes the meaning of a sign by use of varying forms, colours and symbols. However, signs differ greatly i n how explicit their message is. Thus, the meaning of most direction s igns is self-evident, while that of some others is less obvious. The E uropean built-up area sign limits driving speed to 50 km/h, like speed limit signs, but its rectangular form and symbol not associated with speed limit distinguish it clearly from standard speed limit signs. Al so, the function of the built-up area sign is more complex than the on e of speed limit signs: the built-up area sign both limits speed and i nforms about entering a built-up area. The purpose of this study was t o investigate whether the built-up area sign is noticed and obeyed as well as speed limit signs. In three held experiments the 50 km/h, 80 k m/h signs and built-up area signs were alternated and speed changes we re measured. Results indicated that the built-up area signs elicit onl y negligible speed responses compared to the speed limit signs while s upervision (visible police car) results in a similar effect for both s igns. The same results were also obtained in the laboratory where slid es about traffic situations were shown to subjects who were asked if i t was necessary to decelerate. These findings suggested that, in contr ast to the built-up area sign, drivers have developed a mental model w hich facilitates more effective noticing of speed limit signs. The bui lt-up sign does not share these facilitating effects, because of its d ual function and symbol and form which are not associated with speed l imits.