Traffic sign comprehension among motorcyclists: the effect of sign display and sign type

The previous studies showed an inconsistent result for the effect of sign type on sign comprehension in different sign display. Therefore, the current study aimed to examine the effect of sign display (symbol+text or symbol-only) and sign type (warning sign, regulatory sign, or command sign) on traffic sign comprehension. A mixed experimental design was conducted on 100 young adult motorcyclists in the Jabodetabek area with two years of riding experience. In each sign, participants were measured their reaction time to comprehend the sign (sign comprehension time) and the accuracy of the meaning of the sign (sign comprehension level). The result showed that the effect of sign display depends on the type of traffic signs both in sign comprehension time and comprehension level. Based on the results, it can be inferred that further training and socialization are needed to increase riders’ comprehension of all types of traffic signs.


1.
Introduction Each year, approximately 1.3 million people die due to traffic accidents, as one of the main causes of death in the world, including in Indonesia [1].The number of traffic accidents in Indonesia from 2015 to 2019 increased by 4,87 percent each year [2].Among all road users, motorcyclists as the largest road users, contributed to the most traffic accidents in the last decades [2][3][4].This high number of traffic accidents among motorcyclists could be caused by the lack of discipline in obeying traffic regulations, the lack of road safety knowledge, and the low level of traffic signs comprehension [5][6][7].
The limited knowledge of comprehending traffic signs could be one of the crucial factors that contributed to accidents among motorcyclists [8,9].Previous research showed that Indonesian motorcyclists, especially those of young age, still need to improve their knowledge regarding traffic signs and regulations [4].Traffic signs are an important factor to control and improve traffic safety [10].Road users are encouraged to comprehend all the roads by using traffic signs.According to Sodikin et al. [11], drivers' comprehension of road signs is crucial because good comprehension indicates that the sign can effectively communicate the message to the driver.However, Dewar et al. [12] stated that 3 Moreover, adding text to the symbol would be more beneficial in helping the driver to learn the meaning of the traffic sign correctly when the sign is less familiar or new [16].
According to Ou and Liu [26], the effect of sign display on sign comprehension also depends on the sign type.An important thing to note from the previous studies on sign display is each study used different types of traffic signs, for example, warning signs [16][17][18], regulatory signs [16], and information/guidance signs [16].Therefore, it could be assumed that sign type is another important factor that needs to be considered in effecting sign comprehension.
According to the Regulation of the Minister of Transportation of the Republic of Indonesia Number 13 Year 2014 [15], there are four different types of traffic signs, i.e. warning signs, command signs, regulatory signs, and guide/information signs.Warning signs are usually used to give awareness to the driver about the potential danger or dangerous places on the road and the nature of the danger.Prohibition Signs state the actions that are prohibited to be performed by road users.Regulatory signs state the orders of road rules and policies to road users.While guidance signs are intended to guide road users and give other necessary information.
Few studies in various countries have proved the effect of sign type on sign comprehension.However, those studies used different sign displays.For example, Al-Madani and Al-Janahi's [27] study among UEA drivers and Yuan and colleagues' [28] studies among drivers in China found that the warning signs were only answered correctly by half of the participants.Another study by Maulina et al. [29] also found that warning signs were less comprehended than regulatory and command signs among Indonesian motorcyclists.Furthermore, this study proved that sign comprehension training is effective for improving sign comprehension among motorcyclists, especially for warning signs.The similarity between these three studies [27-29] was using symbols only as the sign display.Thus, it could be concluded that the comprehension of the warning signs displayed with symbols only was considered very low among road users.This could be due to the warning signs tend to have difficult symbols and thus are hard to understand [30].
On the contrary, Ou and Liu [26] found that warning signs and regulatory signs were better comprehended than guide signs among Taiwanese and Vietnamese motorcyclists.In this study, all signs were displayed by symbol and text.Meanwhile, Sodikin et al. [11] showed that the understanding of warning, regulatory, and command+guide signs, which were displayed by symbol only, was evenly distributed among road users in Indonesian two-wheelers and four-wheelers.
The inconsistent results from the previous studies showed that the effect of sign type on sign comprehension is still inconclusive.Such discrepant results could be due to the different sign display that was used by those studies [11,[26][27][28][29]31].Therefore, the current study aimed to further examine the interaction of sign display and sign type in affecting sign comprehension.

Current study
In the present study, we investigated the effect of sign display and sign type on sign comprehension among motorcyclists.There are a few modifications from the previous studies.First, previous studies used different road users as participants, for example, Koyuncu and Amado [18] used general road users, while Shinar and Vogelzang [16] and Wontorczyk and Gaca [31] used car or professional drivers, and Maulina et al. [17,29,32] focused on motorcyclists.This current research would be focused on motorcyclists, as they have the highest accident rate in Indonesia.
Second, the country where the sign is placed could also contribute to sign comprehension [33,34].Even though traffic signs have the same symbol, they could have different meanings in different countries.For example, the "no bicycles allowed" sign in Europe has a similar design to the "bicycle only" sign in Latin America [35,36].Thus, it is possible to obtain a different result by conducting a study in a different country from the previous studies, especially in non-WEIRD (Western, Educated, Industrialized, Rich, and Democratic) countries [37,38].
Third, very few studies have examined the combination of sign display and sign type on sign comprehension.Previous studies have proven that sign comprehension was influenced by only sign display [16][17][18] or sign type [27-29], individually.By replicating and combining sign display and sign type in a single study, we can examine the certainty of past findings, find an interaction effect, and boost future studies' innovation, especially in the current wave of Open Science where false positive findings are highly prevalent [39].
Fourth, previous studies measured sign comprehension in different ways.For example, few studies used sign comprehension time [18], level [11,[26][27][28][29]32], and both [16,17].In the current study, sign comprehension would be measured by both sign comprehension time and level so that the speed and accuracy in comprehending the sign could be seen comprehensively.
Lastly, familiarity with the sign is one important factor in ergonomic guidelines for the sign to be easily comprehended [13,26,36].Familiar and meaningful traffic signs will be better understood than unusual and unfamiliar ones [34,40,41].Therefore, this study will use unfamiliar traffic sign to control prior experience with the traffic sign.
Based on previous studies, a combination of symbol+text would lead to better comprehension [16][17][18]32].Therefore, it would be predicted that traffic sign comprehension in traffic signs with symbol+text will be higher than the traffic signs with symbol-only.Furthermore, every sign type has its own characteristics, i.e. warning signs are generally harder to understand as they have more complex and abstract symbols than other types of traffic signs [28,30].Thus, it is expected that sign comprehension in warning signs will be lower than in regulatory signs and command signs.Finally, we hypothesized that there is an interaction between sign display and sign type on traffic sign comprehension among motorcyclists.

Participants
Participants consisted of 104 licensed riders (76 males and 28 females) who live in the Jakarta, Bogor, Depok, Tangerang, and Bekasi (Jabodetabek) areas.The inclusion criteria for participants were riders who had a minimum of two years of riding experience and active riders with a minimum of riding five days a week.Participants aged in the range of 19 to 24 years old (Mage=19.96,SD =1.10) were randomly divided into two groups.The road sign with symbol and text group consisted of 52 participants (39 males and 13 females), with an age average of 19.92 (SD =0.92).The road sign symbol-only group consisted of 52 participants (37 males and 15 females), with an age average of 20.00 (SD = 1.25).An online questionnaire (Google Form platform) was used to recruit participants by using a convenience sampling technique.
The minimum detectable effect size of interest was f = 0.125 (or η 2 p= 0.015), calculated based on a sensitivity power analysis using G*Power [42].In the calculation, we used ANOVA: repeated measures, within-between interaction, with an alpha of 0.05, a power of 0.80, the current sample size (N = 104), 2 groups, and 3 measurements.The current study adhered to ethical standards in the 1964 Declaration of Helsinki.Informed consent was provided to the participants before the experiment and a reward would be given after the experiment.

Design
This current study used a mixed design: 2 (sign display: symbol+text vs symbol-only) x 3 (sign type: warning signs vs regulatory signs vs command signs), with sign type being a within-subject factor.The dependent variable is sign comprehension, which was measured by the reaction time to comprehend the sign (sign comprehension time) and the accuracy of the meaning of the sign (sign comprehension level).The sign familiarity was held constant by using only the unfamiliar signs.

Measurement and Apparatus 3.3.1 Computer and Website.
The research was conducted in a computer laboratory, by using a PC, with a 17 inches monitor.A website called Road Sign Avenger (http://roadsignapp.herokuapp.com) was used to conduct the experiment.An example of a website display is shown in figure 1. 5 3.3.2Stimulus.Fifteen traffic signs, consisting of five regulatory signs, five command signs, and five warning signs, were used in the current experiment.There were two variations of sign display, which were symbol only and symbol+text.Examples of sign display variation can be seen in Figure 1.

Sign Comprehension Test.
Sign comprehension time was measured by the time interval between the sign was presented to the participant and their response in pressing the 'next' button on the computer keyboard.The response to the 'next' button indicated that the participant had comprehended the meaning of the road sign.The sign comprehension time was measured in seconds.Meanwhile, the sign comprehension level was measured by the accuracy of the participant's answer in the fields provided on the computer screen when they were asked about the meaning of each sign.Ben-Bassat and Shinar's [10] scoring system was used for the sign comprehension level, with a score of +2 for well-written and complete answers, a score of +1 for correct but incomplete answers, a score of 0 for the wrong answer, and a score of -1 for the opposite answer.

Procedure
In the preparation phase, a survey of 60 licensed riders with the same characteristics as the experiment phase was conducted.The survey was intended to determine the types of traffic signs that will be used in the experiment.To control prior knowledge and familiarity with the traffic signs, we select 30 traffic signs, consisting of 10 regulatory signs, 10 command signs, and 10 warning signs.Participants were asked to rate the familiarity of each sign with a 10-point Likert scale, from 0 (never seen at all) to 10 (always see).Based on survey results, we selected 15 signs that consist of 5 signs for each type of traffic sign.All the signs were chosen based on the lowest mean in each type.We also conducted a pilot study with 20 participants to ensure that the procedures and manipulations were sufficient enough for participants.From the pilot study, we revised the instructions and website appearance.
In the experimental phase, participants had to fill in the informed consent before the study began.The participants did the experiment using a PC individually.There were two groups of participants, which were the sign with symbol+text group or symbol-only group.After the experimenter explained the instructions, participants began the experiment which consisted of 15 traffic signs as the stimulus.In each trial, participants were given a stimulus of traffic signs from the computer.Then, once the participants comprehended the meaning of the sign, they were instructed to press the 'next' button as soon as possible.After they pressed the button, there was a field on the next slide and participants had to type the meaning of the sign.This sequence lasted until the next 15 signs.All the types of traffic signs (warning signs, regulatory signs, and command signs) were displayed to each participant with a counterbalanced sequence.Finally, participants were debriefed and received rewards after completing the experiment.A two-way mixed ANOVA analysis was conducted to analyze the sign comprehension time scores from all the experimental groups.The result showed no statistically significant main effect for sign display (F(1, 102) = 0.16, p = 0.693, η2partial = 0.002), a statistically significant main effect of sign type (F(2, 204) = 10.78,p < 0.001, η2partial = 0.096) and a statistically significant interaction between sign display and sign type (F(2, 204) = 3.96, p = 0.020, η2partial = 0.037).This means the effect of sign display on sign comprehension depended on the sign type.Further simple effect analysis showed that in the symbol+text condition, a statistically significant difference was only found between the regulatory sign and command sign (p = 0.001), in which the regulatory sign (M = 23.98,SD = 14.42) was comprehended significantly faster than the command sign (M = 30.87,SD = 18.34).Meanwhile, in the symbol-only condition, a statistically significant difference was found between all sign types (all ps < 0.05).The regulatory sign (M = 20.85,SD = 11.99) was comprehended significantly faster than the command sign (M = 26.46,SD = 15.05), and the warning sign (M = 31.75,SD = 25.49),whereas the command sign was significantly faster than warning signs (see figure 2).Thus, the symbol-only sign would be comprehended fastest in regulatory sign, while the longest comprehension time was in warning sign.A two-way mixed ANOVA analysis was also conducted to analyze the sign comprehension level scores from all the experimental groups.The results showed a statistically significant main effect of display (F(1, 102) = 4.90, p = 0.029, η2partial = 0.046), a main effect of sign type (F(2, 204) = 68.31,p < 0.001, η2partial = 0.401), and interaction between sign display and sign type (F(2, 204) = 7.25, p = 0.001, η2partial = 0.066).Following this interaction, additional simple effects analyses were run, and the result showed that there was a statistically significant difference in comprehension level between regulatory sign, command sign, and warning sign in both symbol+text condition and symbol-only condition (all ps < 0.05).The highest comprehension level was found in regulatory sign (Msymbol+text = 8.08, SDsymbol+text = 2.53; Msymbol-only = 8.46, SDsymbol-only = 1.94), while the warning sign (Msymbol+text = 6.06,SDsymbol+text = 1.64;Msymbol-only = 4.48, SDsymbol-only = 1.93) received the lowest comprehension level (see figure 3).Furthermore, simple effect analysis also revealed that there was no statistically significant difference in sign comprehension level between symbol+text and symbol-only (all ps > 0.05) in both regulatory and command sign.A distinct finding was seen for the warning sign, in which symbol+text was statistically significantly comprehended correctly than the symbol-only condition (p < 0.05; see table 2.).

Figure 3. The average sign comprehension level on each sign type for symbol+text and symbol-only condition
Based on all the significant results above, it could be concluded that the current study (N= 104) had good power because the sensitivity power for each result was higher than the minimum (η 2 partial = 0.015).

Discussion
The study aimed to investigate the effect of two sign displays (symbol+text vs symbol only) and three types of traffic signs (regulatory sign vs command sign vs warning sign) on sign comprehension among motorcyclists.Our study found that sign display had a main effect only on sign comprehension level, but not on sign comprehension time.Moreover, a significant main effect of sign type on sign comprehension time and level was also found.Finally, an interaction effect between sign display and sign type was found to be significant in both sign comprehension time and level.
In sign comprehension time, the current study found that the regulatory sign was comprehended the fastest while the slowest was the command sign in the symbol+text condition.A similar result was found in the symbol-only sign condition in which the regulatory sign was comprehended the fastest while the warning sign needed the longest time to comprehend.Based on these results, the regulatory sign was the sign type that is comprehended the fastest in symbol+text and symbol-only conditions.This result is in line with a study by Ou and Liu [26] that sign comprehension was better for the common sign in Taiwan which is the regulatory signs.The possible explanation for why the regulatory sign could be comprehended faster than other signs is related to the characteristic of the regulatory sign which is it contains more concrete symbols.Concrete symbols consist of objects that are often seen in people's daily lives, so the information is already stored in their memory.Thus, it would take a little time for the person to recognize and comprehend the information.Past studies indicated that recognition of concrete stimuli (e.g.faces and everyday objects) was better than abstract stimuli, for example, pictures of snow crystals and inkbolt patterns [43][44][45][46].Therefore, in this study, the sign comprehension time in unfamiliar regulatory sign would still be faster than other signs because it contains concrete symbols that could help the riders to quickly comprehend the meaning.
Another interaction pattern between sign display and sign type was found in the sign comprehension level.In both symbol+text and symbol-only conditions, the highest sign comprehension level was found in the regulatory sign, while the lowest was found in the warning sign.The symbol in the warning sign was considered more abstract and less familiar than other signs, so the riders need more effort to comprehend the warning signs [28,29].Complex and unfamiliar symbol could cause confusion to the riders because there is no prior knowledge in their memory that could help the riders to comprehend the meaning of the symbol on the sign.This resulted in the rider not knowing and/or misunderstanding the meaning of the sign.This explains why in this study, the comprehension level of warning sign, which consist of abstract symbol, is lower than other signs.One way for the riders to accurately comprehend an abstract symbol is by making them more familiar with the symbol.According to Shen et al. [44], a complex and abstract symbol will become more familiar if it is exposed for a long period of time.Therefore, increasing the familiarity of the symbol can make the sign easier to be identified and decrease the error rate.
Furthermore, in the current study, the result showed that in the warning sign, symbol+text condition produced a significantly higher sign comprehension level than symbol-only condition.This result was in line with a previous study by Maulina et al. [32] that found sign comprehension level for the warning sign in symbol+text and text-only conditions was higher than in symbol-only condition.As mentioned before, the warning sign consists of an abstract symbol.Adding text to the abstract and unfamiliar symbol can help the riders to comprehend the meaning of the sign because signs with no text elicit confusion for participants to interpret the symbols.The information could be remembered more easily when it contains symbol and text because that combination enhances the meaning of each symbol and text [47].In unfamiliar signs, riders need to associate the symbol and text to comprehend the meaning of the sign, thus the sign comprehension level of the symbol+text sign will be higher than the symbol-only sign.
It is important to note several limitations to the study.First, participants in this study only involve young riders (19-24 years old).Age is an important factor in riders' sign comprehension and younger drivers (age less than 25 years old) had the lower traffic signs' familiarity and comprehensibility than older riders [48].Therefore, future study needs to include age in examining the effect of the sign characteristic on sign comprehension.Second, the current study used unfamiliar traffic signs.Since familiarity is one of the important factors that contribute to riders' ability to comprehend the meaning of the sign, future studies should compare the comprehension of familiar and unfamiliar signs to test the consistency of the findings.Lastly, our study was conducted in laboratory experimental design, thus a field experiment study is needed to enhance the external validity of the study.Adding environmental context, which is done in field experiment, had a significant positive effect on sign comprehension because the information given by a road sign is context-dependent [49,50].Thus, it can increase the driver's understanding of traffic signs.
In conclusion, the low comprehension of unfamiliar signs can be overcome by providing additional text on the unfamiliar signs or through training.Sign comprehension training for unfamiliar signs, especially warning signs, was proven to be effective in increasing the sign comprehension level among motorcyclists [29].Training could be given periodically as a series of processes for the rider's license.

Figure 2 .
Figure 2. The average sign comprehension time on each sign type for symbol+text and symbol-only condition

Table 1 .
Mean and standard deviation of sign comprehension time (N=104).

Table 2 .
Mean and standard deviation of sign comprehension level (N=104).
Nurprasetio I P and Prihutama A 2017 Macro Data Analysis of Traffic Accidents in Indonesia Journal of Engineering and Technological Sciences 49 132-43 [4] Soimun A, Leliana A, Ulmi E I, Ziantono D H and Widyastuti H 2020 Analysis of Student Comprehension of Traffic Signs (Analisis Pemahaman Pelajar pada Rambu Lalu Lintas) Jurnal Teknologi Transportasi Dan Logistik 1 91-100