Increasing the default interletter spacing of words can help drivers to read traffic signs at longer distances

• Published in: Accident analysis and prevention 2018-08, Vol.117, p.298-303
• Main Authors: Tejero, Pilar, Insa, Beatriz, Roca, Javier
• Format: Article
• Language: English
• Subjects: Driving performance; Interletter spacing; Reading distance; Traffic signs; Word recognition
• ISSN: 0001-4575; 1879-2057
• DOI: 10.1016/j.aap.2018.04.028

•Interletter spacing is considered as a relevant factor in traffic sign legibility.•The default interletter spacing used in traffic sign design may not be optimal.•The effect of increasing the default spacing is examined using a driving simulation.•An extended spacing increased the distance at which drivers found a target word.•Traffic signs can have room for improvement by increasing the default spacing. Would an increase in the default interletter spacing improve the legibility of words in traffic signs? Previous evidence on traffic sign design and recent studies on the cognitive processes involved in visual word recognition have provided conflicting results. The present work examined whether an increase in the default interletter spacing would improve the search of a word in direction traffic signs. To achieve this objective, twenty-two drivers participated in a driving simulation experiment. They followed a highway route and indicated whether a target place name was present among a set of distractors shown on direction traffic signs along the route. We compared the default interletter spacing of the Spanish “CC Rige” font (which is based on the internationally-used Transport font) and a 2.5-times expanded interletter spacing. The results revealed that the drivers were able to give a correct response at a distance to the traffic sign that was on average longer in the expanded than in the default spacing condition. This advantage in the legibility distance was observed in the absence of significant differences in reading accuracy, gaze behavior, or driving performance measures. Therefore, the evidence provided supports that drivers can benefit from a slight increase in interletter spacing relative to the standard spacing. Some of the design factors influencing this effect are discussed.