The usability of traffic signs
Student thesis: Doctoral Thesis
Guessability, learnability, experienced user performance (EUP), re-usability, and system potential are the five components that would influence the usability of a product. Usability assessments of many different types of consumer products, word processor, public library’s web site, online learning programs, and election incident reporting system have been reported. Traffic signs are probably the best known graphical symbols that we encounter along the roads and highways everyday. However, studies on the usability of traffic signs had never been seen. Three experiments were conducted in this research on investigating the sign usability in a comprehension task. Sign design features (i.e. familiarity, concreteness, simplicity, meaningfulness, and semantic closeness) and some probable user factors were also selected for detailed investigation of their effects on the five components of usability. The first two experiments used Mainland China traffic signs, while the third experiment employed Hong Kong traffic signs. No subjects participated in more than one of the three experiments. Experiment 1 was done for examining the guessability of traffic signs with prospective-users. Mainland China visit experience was a significant factor in sign guessing. The results indicated that when a specific cultural issue is incorporated in a traffic sign, it should be accompanied by supplementary text to reduce the effect of cultural bias. Vehicle ownership had an effect on guessing performance within the groups having intention of being a driver and car game experience. The interaction between attention to traffic signs and traffic incident experience on sign guessability was revealed. But cycling experience, sign knowledge acquisition, and gender were not associated with guessing performance. Semantic closeness was the best predictor of guessability score, followed by familiarity, meaningfulness, concreteness, and simplicity. Experiment 2 was performed on exploring the learnability of traffic signs for prospective-users with three different methods of training. The results showed that training could significantly improve sign comprehension performance. Recall training was preferable for enhancing understanding of traffic signs, followed by recognition training, and then paired-associate learning. It was also shown that some prospective-users could perform at the maximum level in sign comprehension after the meaning of traffic signs has been learned, indicating high learnability of traffic signs. Sign design features of familiarity, concreteness, simplicity, meaningfulness, and semantic closeness were found not related to the training effectiveness. Based on the experimental findings, practical tips for designing more user-friendly sign-training programs were deduced. Experiment 3 addressed the comprehensibility of traffic signs for licensed drivers. An interesting result was found that the comprehension performance of drivers decreased across years of being licensed. It was also revealed that drivers with university or above education level comprehended the signs better. Non-local driving experience would have a negative effect on local sign comprehension. Nevertheless, age group, years of active driving, hours of driving, occupation, local driving test experience, time from last driving, and driving frequency were not significant predictors of sign comprehensibility. On sign features, the results indicated that concreteness, simplicity, and meaningfulness were not the major sign design characteristics that have to be considered. If the traffic signs were learned and encountered frequently, driver performance on sign comprehension was found better. The EUP and re-usability of traffic signs were investigated in the last experiment. The comprehension performance of each frequent driving experienced driver was considered as EUP of traffic signs. From a designer’s perspective, the system potential of traffic signs should be 100% correct. However, the EUP of traffic signs was found not close to the system potential in this study. It was demonstrated that performance on sign comprehension would remain unchanged after a short time or a long time away (i.e. 12 months) from driving, indicating high re-usability of traffic signs. The above three experiments successfully revealed some user factors that affected the usability levels of traffic sign, which illustrated the importance of developing traffic signs with road users in mind. Based on the results of significant and non-significant user factors, particular road user groups who lacked good understanding of traffic signs were identified, thus assisting the related organizations to make better use of traffic education resources. They were pedestrians with traffic incident experience, cyclists, and drivers with non-local driving experience. The above three experiments also showed that the exact cognitive sign features which determine sign usability change as user experience grows. This means that designers should develop and evaluate traffic signs according to the road user groups and relative importance of the sign features. One of the major implications of this research is that the success of effective communication of sign messages to road users might not only relate to the user characteristics but also the signs themselves. Good designers should create and modify traffic signs with prospective-users in mind. If prospective-users can grasp the meaning of a traffic sign, it would probably be understood and memorised easily by experienced road users. In summary, this dissertation (i) provided information and recommendations for the design of ‘easy to understand’ traffic signs and training programs, (ii) identified the specific road user groups who lack good comprehension of traffic signs so as to assist the related organizations to better allocate traffic education resources, (iii) made suggestion for future studies in sign usability, and (iv) would provide some useful guidance for interface designers to design and analyze graphical symbols across various types of consumer and safety products.
- Traffic signs and signals, Traffic engineering