There has been a tendency in recent years for more information to be shown on direction signs which has led to concern that drivers might become overloaded. This study was undertaken to look at the nature of overload, and to suggest ways of preventing it. A photographic survey of direction signs on inter-urban and urban roads indicated how many destinations and how much other information currently appears on signs. A literature survey looked at previous research relevant to overload. A laboratory experiment using the TRL driving simulator measured the response time of drivers to signs with up to 20 destinations. Stack signs, map signs and flag sign arrays were all investigated. Details of the increase in response time when road numbers were added to signs are also given. Data from the experiment was consistent with earlier work on response times for signs with up to 9 names on which current design rules concerning letter heights are based. New tables for letter height which apply to greater numbers of destinations and to different sign types have been developed.

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