The relationship between drivers' personal characteristics and their comprehension of posted signs is investigated in this study. The characteristics considered here include: experience, accident per experience ratio, age, marital status, sex type, nationality, educational background and monthly income. The populations sampled are from Bahrain, Kuwait, Oman, Qatar and United Arab Emirates. A total of 28 posted signs were considered. On an average, drivers comprehended only 56% of the posted signs. Education, monthly income and nationality were related to drivers' comprehension of traffic signs. Western drivers comprehend the signs better than other nationalities. Gulf Cooperation Council States and Arab drivers comprehended the signs less well. Male drivers scored higher than female ones. Age, marital status, experience and accident rates had no effect on drivers comprehension of signs. The results raise serious questions about the applicability of the signing system worldwide. The results indicate that drivers' personal characteristics are primarily associated with their understanding capabilities and not with their accident involvement rates. These findings are believed to be important for the designers of road signs. They are also important for the decision makers for proper allocation of resources in the field of traffic education.