<p>People from some geographical areas are more accustomed to seeing mandatory signs at T-Junctions, whereas in other regions, prohibitory signs are more common. The key question is whether the greater prevalence of one type of sign affects how people draw inferences. Previous studies have shown that, although both types of signs convey the same information, the inferences drawn from them differ. Furthermore, when individuals have sufficient time, they tend to reinterpret possibilities that are not allowed as allowed ones. We conducted two experiments in which participants evaluated diagrammatic traffic scenes on a computer screen featuring mandatory, prohibitory, or redundant (combined) signs at a T-junction. Subsequently, a car moved onto a path that was either allowed or not allowed. The probability of sign appearance varied across three conditions: a higher prevalence of mandatory signs, a higher prevalence of prohibitory signs, or an equal number of each. Participants had to determine whether the manoeuvre was not allowed or allowed, and we measured both reaction time and accuracy. The results replicated previous findings with this task: participants evaluated allowed routes more quickly following mandatory signs and routes that were not allowed following prohibitory signs. Interestingly, the relative frequency of signs influenced evaluation speed, but only under specific conditions involving more complex inferences. This pattern disappeared with longer processing times. Overall, the main results align with the model theory of deduction and have both theoretical and practical implications for optimizing signal placement based on drivers’ inferential processing.</p>