ABSTRACT
The road and traffic environment is a regulated system of which traffic signs are an essential and pervasive part. In an urban environment, Summala and Naatanen (1974) observed approximately 14 traffic signs per kilometer (i.e., on average 1.4 signs every 100 m), so the term pervasive is hardly an overstatement. As described elsewhere in this book, signs may be classed as mandatory (directing what must or must not be done), warning (advising of a potential hazard ahead), and directional (helping find and follow the desired road). To do their job, traffic signs must give their messages clearly and allow enough time for the driver to see them, understand them, and act appropriately (U.K. Driving Standards Agency, 1992).
