Motorist interpretation of MUTCD freeway lane control signals

The results of a human factors laboratory study designed to investigate current motorist interpretations of lane control signals in a freeway driving environment are presented. Subjects were recruited to view a drawing of a freeway scene that included a sign structure supporting lane control signals over each lane. The type of symbols displayed over the lanes were then varied. Subjects were asked what they believed each signal indicated about the condition of the lane under the signal and what the correct driving response would be to that signal. The results of the study showed that most subjects interpreted the green arrow as indicating that a lane was open and that they would proceed in that lane as normal. The red X was most commonly interpreted as indicating that the lane was closed and that drivers should exit that lane. However, interpretations of the yellow X, defined in the "Manual on Uniform Traffic Control Devices" as a transition signal between the green arrow and the red X, were not as consistent. More important, the interpretation of this symbol was shown to be dependent on what other symbols were present in the overall display configuration at a given point on the freeway.