Marie-Axelle Granié
email: marie-axelle.granie@univ-eiffel.fr

Chloé Thévenet
email: chloé.thevenet@univ-eiffel.fr

Florent Varet
email: florent.varet@univ-lille.fr

Myriam Evennou
email: myriam.evennou@univ-eiffel.fr

Noureddine Oulid-Azouz
email: noureddine.oulid-azouz@ifsttar.fr

Craig Lyon
email: craigl@tirf.ca

Uta Meesmann
email: uta.meesmann@vias.be

Robyn Robertson
email: robynr@tirf.ca

Katrien Torfs
email: katrien.torfs@vias.be

Ward Vanlaar
email: wardv@tirf.ca

Heather Woods-Fry
email: heatherw@tirf.ca

Wouter Van Den Berghe
email: wouter.vandenberghe@vias.be

The Effect of Culture on Gender Differences in Driver Risk Behavior through Comparative Analysis of 32 Countries

Keywords: Gender, Culture, Driver, Violation

We study the effect of culture on gender differences in road user risk behaviors. With the hypothesis that gender differences are not solely due to biological factors, and that the existence and magnitude of differences between gender groups vary according to cultural context, due to differentiated social expectations regarding gender roles, we made a secondary analysis of the ESRA2018 database, comprising 25,459 car drivers (53% male) surveyed by an online questionnaire in 32 countries we distributed in 8 cultural clusters. We analyzed the interactions between gender and culture in reported behavior, personal and social acceptability of 4 violations: drinking and driving, speeding, not wearing a seatbelt and the use of a cellphone while driving. Our results show significant gender differences on risky behaviors and attitudes and complex interactions between gender and culture, with men valuing crash risk behaviors more than women do in all cultural clusters observed.

Interactions between gender and culture is more frequent on declared behaviors and personal acceptability than on perceived social acceptability and on drinking and driving and not wearing a seatbelt more than on speeding and the use of cellphone while driving. In addition, gender differences are greater in Western countries than in the Global South. We discuss these gender differences in road user behaviors, attitudes and perceptions as results of an interaction between biological and evolutionary factors and cultural and social factors. These results could be useful to better tailor road safety campaigns and education.

INTRODUCTION

Road crashes are one of the leading causes of death worldwide and gender is one of the most important explanatory factors for the observed individual differences. The question that remains is whether these differences between males and females are related to biological factors or to social constructions. This issue is important because, if these differences are socially constructed, then policy measures can be put in place to try to mitigate them. To answer this question, we analyzed observable cultural variations in gender differences in behaviors and attitudes towards four crash risk driving behaviors (drinking and driving, speeding, driving without seatbelt, talking on a hand-held phone while driving) through a secondary analysis of the ESRA 2 database of 32 countries. The results show that gender differences do indeed vary according to cultural context, but men everywhere engage in riskier behaviors than women. This finding is in line with the validation of a dual risk factor for men. The social valuation of risky driving behavior as a sign of masculinity, particularly in Western countries, enhances the potential for innate biological differences between the two sexes. The challenge is to reduce this gap by getting drivers of both sexes to be more cautious, and less masculine, on the road.

LITERATURE REVIEW

Road crashes, in 8th place among the causes of death in the world [START_REF]Global status report on road safety: time for action[END_REF], remain a significant public health issue, where the role of gender is undeniable. Males are more often involved in road crashes than females (2), while females represent 51% of the world's population, but only 24% of road deaths [START_REF]Traffic Safety Basic Facts on Gender[END_REF]. In addition, gender differences in the risk of fatal crashes are highly dependent on age. Young men under the age of 25 account for 73% of all road deaths and are three times more involved in road crashes than women [START_REF]Global status report on road safety 2018[END_REF]. However, this gender gap decreases with age, being greater for drivers aged 16 to 39 (with males drivers 1.6 to 2.5 times more likely to be at risk than females drivers) than for drivers aged 40 to 59 (with an increased risk of 1.2 to 1.3 times for males) [START_REF]Global status report on road safety 2018[END_REF][START_REF] Massie | Traffic accident involvement rates by driver age and gender[END_REF]. This gender gap disappears even among drivers over 60 years of age [START_REF] Massie | Traffic accident involvement rates by driver age and gender[END_REF]. Some authors explain that gender differences in road crashes are mainly related to the fact that men drive more and over longer distances than women [START_REF] Laapotti | What are young female drivers made of? Differences in attitudes, exposure, offences and accidents between young female and male drivers[END_REF]. Although male and female mobility patterns tend to converge in high-income countries, differences persist in all the countries in terms of complexity of activity patterns and the modes of travel used [START_REF] Duchène | Gender and Transport[END_REF]. However, the gender difference in fatal crashes persists, even when this difference in trip type and mileage is considered [START_REF] Martin | Différences entre les hommes et les femmes face au risque routier[END_REF], particularly among younger drivers [START_REF] Wylie | Young female drivers in New Zealand[END_REF][START_REF] Doherty | The situational risks of young drivers: the influence of passengers, time of day and day of week on accident rates[END_REF][START_REF] Williams | Teenage drivers: patterns of risk[END_REF].

The observed gender differences in road crashes may also be partly explained by males greater involvement in risky and illegal behavior [START_REF] Barr | Gender differences in perceptions and self-reported driving behaviors among teenagers[END_REF], their greater sensation-seeking [START_REF] Cestac | Young drivers' sensation seeking, subjective norms, and perceived behavioral control and their roles in predicting speeding intention: How risk-taking motivations evolve with gender and driving experience[END_REF] and the lower use of safety measures that could protect them (e.g. seat belts, helmets) [START_REF] Fernandes | A systematic investigation of the differential predictors for speeding, drink-driving, driving while fatigued, and not wearing a seat belt, among young drivers[END_REF]. Young males, in particular, tend to engage more frequently than females in offending driving behaviors (speeding, not wearing seatbelts, drinking and driving) that may contribute to their increased crash risk [START_REF] Ouimet | Perceived Risk and Other Predictors and Correlates of Teenagers' Safety Belt Use During the First Year of Licensure[END_REF][START_REF] Dejoy | An examination of gender differences in traffic accident risk perception[END_REF][START_REF] Hanna | Fatal crashes involving young unlicensed drivers in the US[END_REF].

Males -especially young males -perceive less risk than females in different driving situations [START_REF] Bergdahl | Ethnic and gender differences in attitudes toward driving[END_REF] and declare more risky behavior on the road [START_REF] Bina | Risky driving and lifestyles in adolescence[END_REF]. Males are more likely to perceive themselves as immune to risks that threaten others than females, and to overestimate their driving skills [START_REF] Glendon | Age and Gender Differences in Perceived Accident Likelihood and Driver Competences[END_REF]. Males consider risky behavior as less serious than females [START_REF] González-Iglesias | Driving anger and traffic violations: Gender differences[END_REF], and feel less concerned about the personal consequences of risk [START_REF] Cordellieri | Gender effects in young road users on road safety attitudes, behaviors and risk perception[END_REF] or of injuring someone [START_REF] Glendon | Evaluating a novice driver and predriver road safety intervention[END_REF]. For example, nearly one-third of young males report taking risks for pleasure while driving, nearly four times more than females [START_REF] Jessor | Risky driving and adolescent problem behavior: An extension of problem behavior theory[END_REF]. Conversely, females feel more concerned by all road safety problems [START_REF] Butters | Gender differences and demographic influences in perceived concern for driver safety and support for impaired driving countermeasures[END_REF]. They perceive greater risks in speeding [START_REF] Obst | Age and gender comparisons of driving while sleepy: Behaviours and risk perceptions[END_REF], for example, and in using their phone while driving [START_REF] Struckman-Johnson | Gender differences in psychosocial predictors of texting while driving[END_REF].

Classically, the tendency for males to take risks is explained by a combination of biological and evolutionary theories [START_REF] Granié | Accidentalité, comportements à risque, accès au permis de conduire: quelles différences entre femmes et hommes? In: La sécurité routière en France : quand la recherche fait son bilan et trace des perspectives[END_REF]. Males are thought to have a higher rate of sensation seeking and take more risks than females because they produce more androgens [START_REF] Zuckerman | Psychobiology of personality[END_REF] and/or because of their reproductive function [START_REF] Daly | Evolutionary psychology and family violence[END_REF]. The most recent research thus attempts to show both the biological and social origins -innate and acquired -of gender differences in risk-taking.

Brown [START_REF] Brown | Sex Differences in First-Time DWI Offenders: Role of Alcohol and Neurobiological Factors[END_REF] identifies a double risk factor for the male population. The male biological sex affects hormones, the effect of alcohol and neurocognitive development, whereas the masculine psychosocial gender role brings a cultural, social and individual value to risk-taking. Females in contrast have a double protective factor against the risk of crashes: being biologically female and also the feminine gender role that constitutes obstacles to the biological and social factors that explain risk-taking. Indeed, some studies highlight the fact that gender differences on the road could be explained in terms of gender roles resulting from socialization [START_REF] Granié | Accidentalité, comportements à risque, accès au permis de conduire: quelles différences entre femmes et hommes? In: La sécurité routière en France : quand la recherche fait son bilan et trace des perspectives[END_REF]. Gender roles and gender stereotypes refer to a set of social beliefs about what a male and a female should be in a given society [START_REF] Granié | Accidentalité, comportements à risque, accès au permis de conduire: quelles différences entre femmes et hommes? In: La sécurité routière en France : quand la recherche fait son bilan et trace des perspectives[END_REF]. For Simon and Corbett [START_REF] Simon | Road traffic offending, stress, age, and accident history among male and female drivers[END_REF], gender differences in risky behaviors are simply a reflection of gender role differences, presenting the female role as passive, non-competitive and cautious while the male role is risk-taking, competitive and non-compliant. Norms of masculinity even prescribe a minimization of danger, coupled with reckless behavior [START_REF] Struckman-Johnson | Gender differences in psychosocial predictors of texting while driving[END_REF]. Males then engage in risky behaviors in order to demonstrate their masculinity, adopting typical behaviors and thus departing from feminine behaviors [START_REF] Courtenay | Behavioral Factors Associated with Disease, Injury, and Death among Men: Evidence and Implications for Prevention[END_REF]. Cars and driving are indeed integral parts of the construction of the masculine identity [START_REF] Walker | Boys on the road : masculinities, car culture, and road safety education[END_REF]. They allow the expression of aggression and competition, both socially expected from men, while being perceived as natural male behaviors [START_REF] Granié | Gender stereotypes associated with vehicle driving among French preadolescents and adolescents[END_REF]. Thus, some research shows that, regardless of age, sex differences in risk-taking are explained more by individuals' conformity to gender roles (masculinity and femininity) than by biological sex [START_REF] Granié | Effects of gender, sex-stereotype conformity, age and internalization on risk-taking among adolescent pedestrians[END_REF][START_REF] Özkan | What causes the differences in driving between young men and women? The effects of gender roles and sex on young drivers' driving behaviour and self-assessment of skills[END_REF][START_REF] Oppenheim | Can traffic violations be traced to gender-role, sensation seeking, demographics and driving exposure?[END_REF]. As Brown's work [START_REF] Brown | Sex Differences in First-Time DWI Offenders: Role of Alcohol and Neurobiological Factors[END_REF] suggests, gender differences in risk taking could be due to biological factors but could also vary across cultures and with socially expected female and male gender roles. As gender stereotypes and gender roles vary across cultures, the behaviors expected of males and females may also vary. For example, Lund and Rundmo [START_REF] Lund | Cross-cultural comparisons of traffic safety, risk perception, attitudes and behaviour[END_REF] argue that the fact that females are more risk-sensitive and perceive a higher risk on the road than males is only valid in high-income countries. Indeed, in Ghana, the perception of risk is similar between males and females, because as inhabitants of developing countries, they are more accustomed to risk, which could affect their perceptions [START_REF] Flynn | Gender, race, and perception of environmental health risks[END_REF]. Other studies observe that gender differences in several areas can be moderated by culture, and some find paradoxical results. For example, gender differences in personality traits, visuospatial skills or access to scientific disciplines are sometimes greater in high-income countries, with the highest level of gender equality policies, where the gender roles are less differentiated than in the Global South [START_REF] Stoet | The gender-equality paradox in science, technology, engineering, and mathematics education[END_REF]. According to the researchers, in individualistic cultures such as Western countries, individuals would be more likely to explain behavior that conforms to the social norms of their gender group as the expression of individual personal characteristics, rather than conformity to gender norms and social roles. Consequently, gender differences in attitudes and behaviors would be perceived more as free choices and therefore more acceptable in the most individualistic cultures [START_REF] Costa | Gender differences in personality traits across cultures: robust and surprising findings[END_REF].

There is a growing body of research analyzing differences in road user attitudes, perceptions, and behavior across cultures, comparing Global North and Global South countries [START_REF] Üzümcüoğlu | The relationships between cultural variables, law enforcements and driver behaviours across 37 nations[END_REF][START_REF] Özkan | Cross-cultural differences in driving behaviours: a comparison of six countries[END_REF][START_REF] Hussain | Cross-Cultural Differences in Aberrant Driving Behaviors: Comparison of Japanese, Chinese, and Vietnamese Drivers[END_REF][START_REF] Lajunen | The Manchester Driver Behaviour Questionnaire: a cross-cultural study[END_REF]. Studies emphasize the fact that 93% of deaths occur in low-and middle-income countries (4). Furthermore, there are variations between high-and low-income regions in gender differences in crash risk. In low-income regions, gender differences are more pronounced, with females having even fewer car crashes than in wealthier regions, when controlling for exposure [START_REF] Ah | Role of gender in road accidents[END_REF]. To our knowledge however, no study has yet attempted to analyze gender difference variations in driver behaviors and attitudes according to geographical and cultural context.

Studies sometimes include an analysis of gender differences, but only on a country-by-country basis, or on the overall sample [START_REF] Skvirsky | Contributors to young drivers' driving styles -A comparison between Israel and Queensland[END_REF][START_REF] Nordfjaern | Cultural and socio-demographic predictors of car accident involvement in Norway, Ghana, Tanzania and Uganda[END_REF][START_REF] Mcilroy | How do fatalistic beliefs affect the attitudes and pedestrian behaviours of road users in different countries? A cross-cultural study[END_REF][START_REF] Sârbescu | A cross-cultural analysis of aggressive driving: Evidence from Serbia and Romania[END_REF]. Sometimes researchers analyze only the effect of culture on attitudes and behavior, controlling for the effect of gender [START_REF] Özkan | Cross-cultural differences in driving behaviours: a comparison of six countries[END_REF][START_REF] Ersan | Cross-cultural differences in driver aggression, aberrant, and positive driver behaviors[END_REF][START_REF] Üzümcüoğlu | How drivers perceive traffic? How they behave in traffic of Turkey and China?[END_REF]. Only one study to date analyzes gender differences in several countries [START_REF] Cordellieri | Gender effects in young road users on road safety attitudes, behaviors and risk perception[END_REF], but only on young driver behaviors and attitudes. However, again, gender analysis is only carried out on the overall sample and by country. No study to our knowledge has so far compared gender differences with regard to road risk attitudes and behaviors in different cultural contexts.

Comparing different cultural contexts will help to understand whether differences between males and females in road risk attitudes and behaviors are related solely to biological factors or also to psychosocial factors. If gender differences are also related to psychosocial factors, then these differences could vary across cultures, being more or less pronounced depending on the cultural context.

The objective of this study is therefore to explore whether gender differences in crash risk behavior self-reported by drivers are the same regardless of cultural context or vary according to it. Based on our review of the literature, we hypothesize that gender differences are not solely due to biological factors, and that the existence and magnitude of the differences between gender groups in terms of driver risk behaviors and attitudes vary according to cultural context, due to differentiated social expectations regarding gender roles.

METHODS

The purpose of this article is to explore the cultural variations of gender differences in reported risk behaviors while driving, by secondary analysis of the database from the ESRA project. The ESRA project (E-Survey of Road users' Attitudes) aimed at collecting comparable (inter)national data on road users' opinions, attitudes and behaviors with respect to road traffic risks. It is a joint initiative of road safety institutes, research organizations, public services and private sponsors, across 46 countries. The initiative is funded by the partners' own resources. The first wave of the second edition of the ESRA survey (ESRA2) was carried out in 2018 and conducted in 32 countries across five continents.

Questionnaire

All of the ESRA2 30 partners1 jointly developed a questionnaire in English, that each partner then translated into its own national language versions. The questionnaire explored several dimensions of individual behavior and beliefs: self-declared behaviors, acceptability (personal and social), perceived behavior control, risk perception, support for policy measures, opinions of traffic rules and penalties, and perception of enforcement. The questionnaire addresses several road safety issues: driving under the influence of alcohol and drugs, speeding, driving without wearing a seatbelt and child restraint systems, distraction and fatigue (including by using the cellphone and Internet access while driving).

Most of the survey questions used Likert scales that assume responses can be linearly measured. To determine reported behavior, we used a scale of 1 to 5 with 1 being never and 5 being almost always using a question such as: "Over the last 30 days, how often did you as a car driver drive without wearing your seatbelt?" To determine the social acceptability of specific behaviors we used a scale of 1 to 5 with 1 being unacceptable and 5 being acceptable using a question such as: "Where you live, how acceptable would most other people say it is for a car driver to not wear a seatbelt while driving?".

We also collected several demographic data: gender, year of birth, level of education, type of employment, frequency of use of different modes of transport. The age was then calculated and distributed into 6 groups (18-24y, 25-34y, 35-44y, 45-54y, 55-64y, 65y+).

All information on the questionnaire is available on www.esranet.eu. We describe the items observed and the corresponding scale at the beginning of the presentation of the results of each of our questions about risky driving behavior.

Procedure and sample

The ESRA survey is a self-administered, online questionnaire using an access panel of participants. Four market research agencies organized the fieldwork and administered the survey to a representative sample (at least N=1,000) of the national adult population (18+) in each participating country. They collected the data in November and December 2018. The ESRA2_2018 survey in total collected data from 35,036 road users (50.2% females) in 32 countries.

Data used for this secondary analysis and limitations

The aim of the ESRA project was not to explore gender differences between countries, but to collect comparable (inter)national data on road users' opinions, attitudes and behavior with respect to road traffic risks. This has several implications for the data available for the secondary analysis presented here to analyze the interactions between gender and culture on driver attitudes and behavior and some limitations of the analyses should be underlined.

First, for this secondary analysis, we have chosen to group these 32 countries into cultural clusters, using the clusters proposed by the GLOBE Project [START_REF] House | Culture, leadership, and organizations: The GLOBE study of 62 societies[END_REF]. This approach is more helpful for summarizing similarity and differences among countries that result from meaningful cultural dimensions than comparing societies one by one. These clusters are based on the positioning of 61 countries on 9 cultural dimensions (e.g., in-group collectivism, institutional collectivism, gender egalitarianism, power distance), derived from Hofstede's work [START_REF] Hofstede | Culture's consequences: Comparing values, behaviours, institutions, and organizations across nations[END_REF]. The 32 countries represented in the ESRA data were thus distributed for our study into 8 cultural clusters (presented in alphabetic order):

-Anglo group: Australia, Canada, Ireland, United Kingdom, USA; -Asia group: India, Japan, Republic of Korea; -East Europe: Czech Republic, Greece, Hungary, Poland, Serbia, Slovenia; -Germanic group: Austria, Belgium, Germany, The Netherlands, Switzerland; -Latin Europe: France, Italy, Portugal, Spain; -Middle East and Maghreb: Egypt, Morocco, Israel; -Nordic group: Denmark, Finland, Sweden -Sub Saharan Africa: Kenya, Nigeria, South Africa.

Second, the survey targeted all road users: passenger vehicle drivers but also other road users including cyclists, pedestrians, and moped and motorcycle riders. To control for the effect of mode of travel in this study, for this analysis we focused only on participants who reported driving a car (thermic, electric or hybrid), at least a few days a month during the past 12 months (72.66% of the sample: 74.9% of males and 64.8% of females). Table 1 shows that the resulting sample consists of 25,459 individuals: 13,540 males and 11,919 females (53.18% and 46.82% of the sample respectively) equally distributed in the eight cultural groups studied. Third, we did not consider all the attitudes and behaviors measured in the survey. This secondary analysis focuses only on the behaviors reported by participating drivers, and regarding only the four crash-risk behaviors that are addressed in each of the dimensions explored in the questionnaire (self-reported behaviors, attitudes, perceptions). Each of these behaviors is subject to a legal prohibition in all the countries surveyed: driving under the influence of alcohol, excessive speed outside built-up areas, non-use of safety belt and mobile phone use while driving.

Fourth, several variables that may interact with gender group and culture need to be controlled for. Age is likely to interact with gender on the variables measured and age distribution may vary between countries: we took this into account in the statistical analyses through the age category to control for its effect. Exposure (i.e. number kilometers driven) varies according to gender group, is likely to influence the variables measured (behavior, risk acceptance) and its level may vary according to the countries observed for both sexes. As exposure in terms of kilometers driven as a driver is unfortunately not available in the database, we have tried to consider its effect through driving frequency. This frequency is measured using a Likert-type scale, from 1 corresponding to using the vehicle as a driver at least 4 times a week to 3 corresponding to using the vehicle a few days a month. The interest of this variable was very limited, since information on distances travelled, type of network used, speed or type of vehicle was not available. The information is not precise: we cannot deduce from this variable the number of kilometers driven (an individual may drive more or less frequently on 5 km or 100 km trips), but it at least allows us to differentiate between participants who drive often and those who rarely drive.

Statistical analysis

To ensure an equal representation of countries, we gave an equal weight to each country regardless of their population's size. We weighted the data by genders and six age groups within each country based on population statistics from United Nations data (56).

In order to be able to control for the effect of age and frequency of driving, and to analyze the interactions between gender and cultural group, we carried out two-way analyses of covariance (ANCOVA) to study whether there were significant differences for each violation, in terms of reported behavior, social and personal acceptability between genders and cultural groups after controlling the effect of age and frequency of driving. Several studies support the robustness of the ANCOVA when normality assumptions are violated (for a review see [START_REF] Blanca | Non-normal data: Is ANOVA still a valid option?[END_REF]).

In each ANCOVA we analyzed the effect of two interindividual variables: gender group (2 modalities: males and females) and cultural cluster (8 modalities: Anglo, Asia, East Europe, Germanic, Latin Europe, Middle East, Nordic and Sub Saharan Africa). The age group (6 modalities:18-24, 25-34, 35-44, 45-54, 55-64, 65+) and the frequency of driving (3 modalities: at least 4 days a week, 1 to 3 days a week, a few days a month) were introduced in the analyses as covariables.

As 12 comparisons (3 items on each of the 4 violations) according to gender and culture were made, a Bonferroni correction was applied. At alpha .05, the level of p<0.004 (.05/12) was considered as the cut-off value for significance for ANCOVAs and for Post-Hoc tests. We described and discussed only statistically significant differences in the following section. To interpret the statistically significant main and interactions effects, pairwise comparisons were calculated.

For each statistically significant difference showed by the F test, we give eta squared (²) value as a measure of effect size. The rules of thumb given by Cohen to interpret this indicator of effect size is as follows: the statistically significant difference is considered as small when ²≤.01, medium when ²≤.06, and large when ²≤.14 [START_REF] Cohen | Statistical power analysis for the behavioral sciences[END_REF].

We analyzed the main effects and the interaction effects of gender group and cultural cluster. A statistically significant main effect of the gender group means that the difference between males and females is significant for the whole sample, regardless of the cultural cluster.

A statistically significant main effect of the cultural cluster means that there is a significant difference between cultural clusters for the whole sample, regardless of gender groups. A significant interaction effect between gender and cultural cluster means that the difference between the two gender groups vary across cultural clusters. We described and discussed only statistically significant effects.

RESULTS

Drinking and driving

Participants were asked how often, in the past 30 days, they had driven a motor vehicle when they may have exceeded the legal blood alcohol content (BAC) limit, how acceptable they think most people would say it is, and how personally acceptable they feel it is to drive a motor vehicle after exceeding the legal BAC limit. Table 2 presents the means, standard deviations and F values for the ANCOVAs calculated for the items related to drinking and driving.

Attitudes and behaviors concerning drinking and driving differed between gender groups and between cultural clusters. Indeed, ANCOVAs revealed small but statistically significant differences between the gender groups and between the cultural clusters on declared behaviors and on social and personal acceptability of drinking and driving. For the total sample, males declared higher frequency of drinking and driving, and higher social and personal acceptability than females. The participants from the Nordic cluster showed the least risky attitudes and behaviors while the participants from the Africa cluster showed the riskiest attitudes and behaviors regarding drinking and driving as Table 2 shows.

The differences between males and females in drinking and driving behavior and personal acceptance of speeding varied according to cultural clusters but difference between males and females in perceived social acceptance of drink and drive did not vary from one culture to another. ANCOVAs showed significant interactions between gender groups and cultural clusters on the declared behaviors and the personal acceptability of drinking and driving. Males declared riskier attitudes and behaviors for drinking and driving than females in Western countries whereas there were no statistically significant gender differences in the Asia cluster for the declared behaviors nor in the personal acceptability in the Middle East, African and Asian clusters.

In other words, males did have riskier behaviors and higher personal acceptance of drinking and driving than females in Western countries, but not in the Global South, whereas males perceived it was more socially acceptable to drink and drive than females in all the cultural clusters. Gender differences concerning drinking and driving vary with culture but not for all the variables observed: differences between males and females on personal acceptance and declared behaviors concerning drink and drive vary across cultures whereas gender differences in social acceptability of drink and drive do not vary across cultures.

Excessive speed

Participants were asked how often, in the past 30 days, they had driven faster than the speed limit outside built-up areas (but not on motorways/freeways), how acceptable they think most people would say it is and how personally acceptable they feel it is to speed outside built-up areas (but not on motorways/freeways). Table 3 presents the means, standard deviations and F values for the ANCOVAs calculated for the items related to speeding.

Attitudes and behaviors concerning speeding differed between gender groups and between cultural clusters. Indeed, ANCOVAs revealed small but statistically significant differences between the gender groups and between the cultural clusters on declared behaviors and on social and personal acceptability concerning speeding. For the total sample, males declared more frequent speeding behaviors and higher social and personal acceptability of speeding than females. Moreover, participants from the Nordic and Germanic cultural clusters had the riskiest attitudes and behaviors in terms of speeding, while participants from African and Asian cultural clusters had the least risky behaviors and attitudes of all cultural clusters.

The differences between males and females in speeding behaviors and perceived social acceptance of speeding did not vary according to cultural clusters but difference between males and females in personal acceptance of speeding varied from one culture to another. Indeed, ANCOVAs revealed statistically significant interactions between gender group and cultural clusters on the personal acceptability of speeding, but not on the declared behaviors nor on the perceived social acceptability. The gender differences in personal acceptability of speeding were statistically significant for all the cultural clusters, except for the African cluster.

In other words, males perceived more than females that it was personally acceptable to speed in all clusters except for African countries. On the other hand, males exhibited riskier behaviors in speeding than females and higher perceived social acceptance for driving in all cultures. Only gender difference concerning personal acceptance of speeding varies with culture, whereas gender differences in declared speeding behaviors and in social acceptance do not vary across cultures.

Not wearing a seatbelt

Participants were asked how often, in the past 30 days, they had driven without wearing their seatbelt, how acceptable they think most people would say it is, and how personally acceptable they feel it is to not wear a seatbelt while driving. Table 4 presents the means, standard deviations, and F values for the ANCOVAs calculated, for the items related to driving without wearing a seatbelt.

Attitudes and behaviors concerning driving without wearing a seatbelt differed between gender groups and between cultural clusters. Indeed, ANCOVAs revealed small but statistically significant differences between the gender groups and between the cultural clusters on declared behaviors and on social and personal acceptability of driving without a seatbelt. For the total sample, males were more likely than females to declare driving without a seatbelt and to perceive greater social and personal acceptability for not wearing a seatbelt. Moreover, participants from English-speaking countries were more concerned and less accepting of driving without wearing a seatbelt, whereas the participants from Middle East and African clusters accepted and reported not wearing a seatbelt the most, for both gender groups.

Differences between males and females in risky personal attitudes and behaviors concerning driving without a seatbelt varied from one cultural cluster to another, but not the difference between males and females in social acceptability of this risky behavior. Indeed, ANCOVAs revealed statistically significant interactions between gender groups and cultural clusters on the declared behaviors and personal acceptability, but not on the social acceptability of driving without a seatbelt. Males had significantly riskier personal acceptability and behaviors than females in the Anglo, Germanic, Nordic and East Europe clusters, but not in the Middle East and Asian cultural clusters.

In other words, males were more likely to drive without wearing a seatbelt and were more accepting of this risky behavior than females, in Western countries but not in the Global South.

However, males perceived it was more socially acceptable to drive without wearing a seatbelt than females in all cultures. Gender differences concerning driving without wearing a seatbelt vary with culture but not for all the variables observed: differences between males and females on behaviors and personal acceptability of driving without a seatbelt vary across cultures whereas gender differences in perceived social acceptability of driving without a seatbelt do not vary across cultures.

Talking on a hand-held phone while driving

Participants were asked how often, in the past 30 days, they had talked on a hand-held phone while driving, how acceptable they think most people would say it is, and how personally acceptable they feel it is to talk on a hand-held phone while driving. Table 5 presents the means, standard deviations and F values for the ANCOVAs, calculated for the items related to talking on a phone while driving.

Attitudes and behaviors concerning driving while talking on a hand-held phone differed between gender groups and between cultural clusters. Indeed, ANCOVAs revealed small but statistically significant differences between gender groups and between cultural clusters on declared behaviors and on social and personal acceptability. For the total sample, males declared greater use and acceptance of cellphone while driving and perceived it more as socially accepted than females. Moreover, Anglo cluster is the cluster that used and accepted the less the use of cellphone while driving, whereas Middle East and Africa cultural clusters showed the highest use and acceptability, for both gender groups (Table 5).

Differences between males and females did not vary from one cultural cluster to another concerning risky attitudes and behaviors towards use of cellphone while driving. ANCOVAs revealed no significant interaction between gender and cultural clusters on declared behaviors, or the social and personal acceptability of talking on a hand-held phone while driving.

In other words, gender differences in risky behaviors and attitudes towards using a phone while driving did not vary from one culture to another. Males were more likely to use phones while driving, were more accepting of and perceived it was socially acceptable to use cellphone while driving than females in all cultures. Gender differences concerning using cellphone while driving did not vary with culture: differences between males and females on behaviors and attitudes towards of cellphone use while driving do not vary across cultures.

DISCUSSION

The objective of this paper was to explore the cultural variations of gender differences in self-reported risk behaviors while driving, by secondary analysis of the ESRA2 database on 32 countries distributed in 8 cultural clusters. Based on our review of the literature, our hypothesis was that gender differences are not only due to biological factors and that the existence and magnitude of differences between males and females in terms of risk-taking behaviors and attitudes as drivers vary according to cultural contexts, due to differentiated social expectations about gender roles.

To test our hypothesis, we analyzed gender group influence, cultural group influence and their interaction, controlling for the effect of age and driving frequency, on four risk behaviors (drinking and driving, speeding, driving without a seat belt, and mobile phone use while driving).

Our results show differences between males and females on all behaviors and attitudes observed, and that the existence and magnitude of gender differences vary according to cultural clusters for some of the risky behaviors and attitudes measured. Compared to females, males declared higher personal acceptance of the four risky behaviors explored and these gender differences vary across cultures for three of the behaviors measured (drink and drive, speeding and driving without seatbelt), with greater differences between males and females in Western countries than in the Global South. Males also reported riskier behaviors than females on the four behaviors explored and these gender differences vary across cultures for two of these behaviors (drink and drive and driving without seatbelt), with greater differences between males and females in Western countries than in the Global South. In addition, males perceived greater social acceptance than females of the four risky behaviors explored but none of these gender differences vary across culture. These variations, depending on cultural contexts, in the existence and extent of gender differences in terms of risky driving behavior and attitudes are consistent with our hypothesis, showing that gender differences are not only related to biological factors, but also to social and cultural factors. However, the results show that the relationships between gender differences and cultural factors are complex and that the existence and extent of gender differences in driver risk behavior does not always vary according to cultural contexts.

First of all, all the gender differences we observed were going in the same direction.

Males reported they were more likely to violate the four specific traffic situations we asked about and were more likely to perceive such violations as socially and personally acceptable in all regions we studied. Thus, males always show a greater propensity for risk than females, whether or not we observe cultural variations in these gender differences. The more prevalent risk behaviors and attitudes of men in all regions for almost all behaviors support the explanation of more stable and generalized gender differences across cultures. This stability in the direction of the gender differences, common to all the cultural contexts studied, could show that gender differences are not only the result of culture but also seem to stem from biological, physiological and evolutionary factors. As mentioned above, this greater attractiveness of males to risk in all the cultural contexts studied could be explained by the influence of androgenic hormones leading to increased sensation seeking [START_REF] Zuckerman | Psychobiology of personality[END_REF] or a means of positively distinguishing themselves in the competition between males to attract females [START_REF] Daly | Evolutionary psychology and family violence[END_REF]. In this sense, these results support the idea from Brown et al. [START_REF] Brown | Sex Differences in First-Time DWI Offenders: Role of Alcohol and Neurobiological Factors[END_REF] of a double risk factor among males linked both to the biological sex and to the social and cultural gender.

Second, we found that gender differences do not always vary according to cultural contexts. These cultural variations did not uniformly affect all dimensions of behavior and all observed risks. Indeed, while gender differences were observed in all cases, they varied more frequently according to cultural contexts for personal acceptability and declared behavior than for social acceptability. In other words, culturally constructed gender roles appear to explain more gender differences in personal risk acceptance and behaviors than gender differences in perceptions of social risk acceptance. These results can be explained by the fact that the perception of social acceptance of risk measured the degree of acceptance of these risk behaviors that participants perceive among drivers where they live, i.e., the descriptive and prescriptive social norms. The results show that although men perceived this social norm as riskier than women, this gender gap did not vary according to gender roles in each cultural context. In contrast, measures of behavior and personal acceptance of risk asked individuals about what they thought and did themselves as drivers. This reflects a dual positioning on the part of individuals. In addition, we did not observe cultural variations in gender differences in all observed risk behaviors. Indeed, we found more interactions between gender group and cultural cluster on drinking and driving and seatbelt use than on speeding, and we found no interaction between gender and culture on any of the three dimensions measured for cellphone use while driving.

Gender differences did exist for speeding and cellphone use while driving but they vary little or not at all according to cultural context. In addition, these violations were perceived as most acceptable in all the cultural clusters and most often reported by both genders than drinking and driving or driving without wearing a seatbelt. Hence, in all cultures, speeding and cellphone use while driving were risky behaviors more accepted by males than by females and were more accepted by individuals of both sexes than drinking and driving and driving without wearing a seatbelt, whose level of acceptance by each of the two gender groups varied according to cultural contexts. In other words, gender roles appear to have less influence on risk behaviors that are widely accepted in all cultures and by both gender groups, where gender differences seem to be primarily the expression of biological and evolutionary factors. Thus, gender roles appear to have more influence on individual positioning and for less widely accepted risk behaviors. Research is still needed to understand why speeding and cellphone use while driving are risky behaviors accepted by drivers from all cultural backgrounds and of both sexes, and to confirm that gender roles affect individual positioning less when social acceptance of the behavior is important.

Finally, the results show that gender differences were more pronounced in Western countries than in African and Eastern countries. This may seem paradoxical since Western countries have the highest level of gender equality policies, and the gender roles are less differentiated than in the Global South [START_REF] Stoet | The gender-equality paradox in science, technology, engineering, and mathematics education[END_REF]. As mentioned above, this could be due to the fact that in the Western countries, conforming to gender roles could be seen as an acceptable individual choice rather than a social obligation or to the fact that women could be more riskadverse in societies that are safer and less accustomed to risk. Future studies should examine whether the extent of gender differences in reported behavior and attitudes could be moderated by the level of the global gender gap index or of car crash rate of the countries surveyed in the ESRA survey. Broader, further analysis on the ESRA2 data should be conducted, integrating more refined indicators of culture already available in the literature, such as those from the World Values Survey (WVS), exploring periodically the cultural values and changes using the Portrait Values Questionnaire (PVQ) from the Schwarz model [START_REF] Schwartz | Refining the Theory of Basic Individual Values[END_REF], or the six dimensions of culture measured in more than 100 countries on the basis of Hofstede's model [START_REF] Hofstede | Cultures and Organizations: Software of the Mind. Revised and expanded 3rd Edition[END_REF].

Furthermore, it seems important to consider that self-reported data are vulnerable to a number of biases [START_REF] Choi | A catalog of biases in questionnaires[END_REF][START_REF] Krosnick | Questionnaire design[END_REF], as misunderstanding of questions or recall error. The desirability bias, i.e. the tendency of respondents to provide answers which present a favorable image of themselves (over-reporting good behavior and/or under-reporting bad, or undesirable behavior) is more pronounced in women than in men [START_REF] Bernardi | Associations between Hofstede's cultural constructs and social desirability response bias[END_REF]. In the specific area of driving behavior, both male and female drivers may be reluctant to admit to illegal or disapproved driving behavior. Or, conversely, men may perceive a greater social desirability for reporting risky or illegal behavior that they may not have engaged in, in order to display "typically male" behavior. Further studies will need to control for this desirability bias, although it can also be seen as an effect of gender roles, also affecting observable behavior [START_REF] Yeung | Stereotype threat increases the likelihood that female drivers in a simulator run over jaywalkers[END_REF][START_REF] Mast | Men Are Hierarchical, Women Are Egalitarian: An Implicit Gender Stereotype[END_REF].

Finally, these initial results need to be confirmed and deepened through specific studies to investigate the interactions between gender and culture in drivers' perceptions, attitudes and risk behaviors, including the monitoring of key variables impacting on gender and culture interactions, such as exposure to risk. All these results show that the influence of gender roles on the behaviors and attitudes of men and women is complex: it varies according to the risky behaviors observed and its dimensions. Gender roles affect individual positions more than social perceptions and less accepted risky behaviors rather than those that are widely accepted socially.

Our results show that cultural variations in gender differences in driving risky behaviors are not directly due to the conformity of all individuals to socially prescribed gender roles, but rather to the way in which each man and woman appropriates these gender roles [START_REF] Granié | Accidentalité, comportements à risque, accès au permis de conduire: quelles différences entre femmes et hommes? In: La sécurité routière en France : quand la recherche fait son bilan et trace des perspectives[END_REF].

CONCLUSIONS

Our aim was to show that gender differences are not only related to biological factors but also to cultural and social factors. Our results show that socially constructed gender roles affect the individual positioning of drivers more than the perception of social norms and affect attitudes and behaviors less when risk behavior is widely socially accepted. Moreover, the greater acceptance of risky behavior by males is observed in all cultures. In addition, compliance with gender roles in risk behavior may be exacerbated in Western countries, where the level of road safety is higher and the need for compliance with traditional social roles is less emphasized. In addition to the effect of gender roles, it seems that male and female behavior is also due to biological and evolutionary factors.

Our results can contribute to education and awareness campaigns and events aimed at reducing risk behaviors. In order to reduce risk behaviors among subsets of the population at risk (particularly men, but also young drivers), it would be appropriate to target the psychological constructs impacting risk behaviors that are most influenced by gender roles. Our results suggest these actions be directed towards men and more widely to target the "male" values and social norms linked to risk behaviors, which influence individual behavior. A recent study [START_REF] Lemarié | Reckless driving promotion and prevention: Priming effects[END_REF] suggests that risky driving behaviors can be reduced by changing the "male" values and social norms that young male drivers associate with them. This finding represents an interesting avenue that should be investigated further in order to implement effective prevention measures based on social norms and gender roles. Finally, for greater effectiveness, road safety actions would also benefit from adopting a targeting strategy, since that individual differences about risky driving may depend on both gender and culture, as well as the type of risk behavior.

Culture can exacerbate these biological gender differences through social norms and beliefs about both sexes, such as the valuing of risk-taking by males. On the contrary, culture can constrain or reduce these differences, through the road safety policies put in place that more or less allow these gendered norms to be expressed through driving behaviors, or by helping individuals to challenge their compliance with the socially constructed aspect of these gender differences. In this sense, studies must continue to explore whether or not national policies to reduce the gender gap in education, economic, and political terms reduce differences in risk behavior between males and females. Indeed, the challenge in reducing this gap in risk behaviors is to get males to value risky behaviors less and to get females not to engage more in such behaviors.

  They position themselves in relation to social norms regarding driving behavior (what each individual accepts and does as a driver in relation to what is acceptable to do where s/he lives), but they also position themselves in relation to social norms regarding gender roles (what each individual accepts and does as a man or woman in relation to what is acceptable to do as a man or woman in their culture). Thus, gender roles would affect individual positioning more than perceptions of social norms.

Table 1 Distribution of the sample over the eight cultural clusters studied according to gender

 1

		Cultural cluster
	Gender	Anglo	Asia	East	Germanic	Latin	Middle	Nordic	Sub	Total
				Europe		Europe	East		Saharan
									Africa
	Males	1866	1173	2453	2846	1731	1172	1116	1183	13540
	Females	1906	901	1993	2664	1571	895	998	991	11919
	% males	49.5	56.6	55.2	51.7	52.4	56.7	52.8	54.4	53.2

Table 2 Mean (and standard deviation) and F value (and eta²) for the ANCOVAs of the reported behavior, the social and the personal acceptability of drinking and driving according to gender and cultural cluster, age and driving frequency controlled

 2

	Cultural cluster	Gender	Reported behavior Social acceptability Personal acceptability
	Anglo	Males	1.26 (0.72)	1.34 (0.84)	1.26 (0.76)
		Females	1.12 (0.49)	1.21 (0.64)	1.12 (0.49)
		Total	1.19 (0.62) b	1.27 (0.75) b	1.19 (0.64) b
	Germanic	Males	1.31 (0.56)	1.53 (0.71)	1.38 (0.62)
		Females	1.14 (0.39)	1.4 (0.65)	1.22 (0.47)
		Total	1.23 (0.49) b	1.47 (0.68) d	1.3 (0.56) c
	Nordic	Males	1.17 (0.54)	1.22 (0.59)	1.19 (0.57)
		Females	1.05 (0.31)	1.19 (0.52)	1.07 (0.33)
		Total	1.11 (0.45) a	1.21 (0.56) a	1.14 (0.48) a
	Latin Europe	Males	1.35 (0.73)	1.48 (0.85)	1.32 (0.69)
		Females	1.14 (0.5)	1.36 (0.82)	1.18 (0.56)
		Total	1.24 (0.64) b	1.42 (0.84) c	1.25 (0.64) c
	East Europe	Males	1.23 (0.57)	1.46 (0.88)	1.24 (0.63)
		Females	1.07 (0.32)	1.33 (0.78)	1.1 (0.38)
		Total	1.16 (0.48) b	1.4 (0.84) c	1.18 (0.54) b
	Middle East and Maghreb	Males	1.23 (0.62)	1.53 (0.96)	1.28 (0.72)
		Females	1.13 (0.53)	1.44 (0.96)	1.3 (0.83)
		Total	1.18 (0.59) b	1.49 (0.96) d	1.29 (0.77) c
	Sub Saharan Africa	Males	1.38 (0.79)	1.62 (1.07)	1.31 (0.77)
		Females	1.17 (0.6)	1.51 (1)	1.22 (0.7)
		Total	1.28 (0.72) c	1.57 (1.04) e	1.26 (0.74) c
	Asia	Males	1.19 (0.59)	1.33 (0.83)	1.24 (0.71)
		Females	1.23 (0.74)	1.3 (0.86)	1.25 (0.79)
		Total	1.21 (0.66) b	1.32 (0.84) b	1.25 (0.74) c
	Total	Males	1.

27 (0.64) 1.44 (0.85) 1.28 (0.68)

		Females	1.13 (0.47)	1.34 (0.77)	1.17 (0.55)
		Total	1.2 (0.57)	1.39 (0.81)	1.23 (0.63)
	F value (²)	Gender	279.67*** (.011)	58.71*** (.002)	127.31*** (.005)
		Culture	23.08*** (.006)	43.50*** (.012)	29.59*** (.008)
		Interaction 8.99*** (.002)	1.44	5.82*** (.002)
	Note. Bonferroni correction was used for pairwise comparisons. For gender, mean values in bold within rows
	indicated scores significantly higher at p<.05. For cultural cluster, mean values with different superscripts (a-e)
	within rows were significantly different at p<.05. The scale used was 1 = never to 5 = almost always for behaviors
	and 1 = unacceptable to 5 = acceptable for acceptability. *  <.05, **  <.01, ***  <.001

Table 3 Mean (and standard deviation) and F value (and eta²) for the ANCOVAs of the reported behavior, the social and the personal acceptability of speeding according to gender and cultural cluster, age and driving frequency controlled Cultural cluster Gender Reported behavior Social acceptability Personal acceptability

 3

	Anglo	Males	2.2 (1.16)	2.13 (1.22)	2 (1.18)
		Females	1.98 (1.06)	1.92 (1.14)	1.69 (0.98)
		Total	2.09 (1.11) b	2.03 (1.18) a	1.85 (1.1) b
	Germanic	Males	2.44 (0.87)	2.5 (0.93)	2.37 (0.93)

Note. Bonferroni correction was used for pairwise comparisons. For gender, mean values in bold within rows indicated scores significantly higher at p<.05. For cultural cluster, mean values with different superscripts (a-d) within rows were significantly different at p<.05. The scale used was 1 = never to 5 = almost always for behaviors and 1 = unacceptable to 5 = acceptable for acceptability. *  <.05, **  <.01, ***  <.001

Table 4 Mean (and standard deviation) and F value (and eta²) for the ANCOVAs of the reported behavior, the social and the personal acceptability of not wearing a seatbelt according to gender and cultural cluster, age and driving frequency controlled Cultural cluster Gender Reported behavior Social acceptability Personal acceptability Anglo Males 1.29 (0.79) 1.43 (0.92) 1.35 (0.86)

 4

		Females	1.16 (0.59)	1.32 (0.76)	1.21 (0.65)
		Total	1.23 (0.7) a	1.38 (0.84) a	1.28 (0.76) a
	Germanic	Males	1.

35 (0.68) 1.75 (0.84) 1.58 (0.76)

  Note. Bonferroni correction was used for pairwise comparisons. For gender, mean values in bold within rows indicated scores significantly higher at p<.05. For cultural cluster, mean values with different superscripts (a-d) within rows were significantly different at p<.05. The scale used was 1 = never to 5 = almost always for behaviors and 1 = unacceptable to 5 = acceptable for acceptability. *  <.05, **  <.01, ***  <.001

	Asia	Males	1.38 (0.79)	1.66 (1.03)	1.52 (0.85)
		Females	1.42 (0.93)	1.63 (1.07)	1.47 (0.9)
		Total	1.4 (0.85) b	1.65 (1.05) b	1.5 (0.87) b
	Total	Males	1.44 (0.84)	1.73 (1.04)	1.53 (0.89)
		Females	1.3 (0.74)	1.6 (0.99)	1.37 (0.76)
		Total	1.37 (0.8)	1.67 (1.02)	1.45 (0.83)
	F value (²)	Gender	142.35*** (.006)	74.41*** (.003)	172.85*** (.007)
		Culture	100.02*** (.027)	71.83*** (.019)	31.72*** (.009)
		Interaction	5.17*** (.001)	2.46	3.43* (.001)
		Females	1.22 (0.54)	1.6 (0.78)	1.4 (0.64)
		Total	1.29 (0.62) a	1.67 (0.81) c	1.49 (0.71) b
	Nordic	Males	1.37 (0.84)	1.69 (0.97)	1.6 (0.97)
		Females	1.16 (0.56)	1.48 (0.81) b	1.32 (0.72)
		Total	1.27 (0.73) a	1.59 (0.91)	1.46 (0.87) b
	Latin Europe	Males	1.31 (0.76)	1.59 (0.94)	1.47 (0.86)
		Females	1.19 (0.6)	1.53 (0.98)	1.34 (0.73)
		Total	1.25 (0.69) a	1.56 (0.96) b	1.41 (0.81) b
	East Europe	Males	1.47 (0.83)	1.94 (1.18)	1.62 (0.99)
		Females	1.35 (0.75)	1.81 (1.17)	1.42 (0.78)
		Total	1.41 (0.8) b	1.88 (1.18) c	1.53 (0.91) b
	Middle East and	Males	1.6 (1)	1.89 (1.16)	1.58 (0.98)
	Maghreb	Females	1.5 (1.03)	1.76 (1.25)	1.53 (1.01)
		Total	1.55 (1.01) c	1.83 (1.2) c	1.56 (0.99) b
	Sub Saharan Africa	Males	1.9 (1.07)	1.95 (1.21)	1.49 (0.85)
		Females	1.64 (1.03)	1.75 (1.19)	1.4 (0.85)
		Total	1.78 (1.06) d	1.86 (1.2) c	1.44 (0.85) b

Table 5 Mean (and standard deviation) and F value (and eta²) for the ANCOVAs of the reported behavior, the social and the personal acceptability of making a phone call while driving according to gender and cultural cluster, age and driving frequency controlled

 5 Bonferroni correction was used for pairwise comparisons. For gender, mean values in bold within rows indicated scores significantly higher at p<.05. For cultural cluster, mean values with different superscripts (a-g) within rows were significantly different at p<.05. The scale used was 1 = never to 5 = almost always for behaviors and 1 = unacceptable to 5 = acceptable for acceptability.

	Cultural cluster	Gender	Reported behavior Social acceptability Personal acceptability
	Anglo	Males	1.4 (0.87)	1.56 (1.04)	1.43 (0.94)
		Females	1.33 (0.77)	1.5 (0.94)	1.32 (0.76)
		Total	1.37 (0.82) a	1.53 (0.99) a	1.37 (0.86) a
	Germanic	Males	1.54 (0.78)	1.72 (0.83)	1.47 (0.69)
		Females	1.4 (0.67)	1.64 (0.8)	1.4 (0.65)
		Total	1.47 (0.73) c	1.68 (0.82) b	1.44 (0.67) b
	Nordic	Males	1.61 (0.95)	1.88 (1.03)	1.69 (1)
		Females	1.51 (0.87)	1.85 (1.05)	1.53 (0.88)
		Total	1.56 (0.91) d	1.87 (1.04) d	1.61 (0.95) c
	Latin Europe	Males	1.47 (0.79)	1.65 (0.95)	1.42 (0.76)
		Females	1.35 (0.75)	1.62 (1.03)	1.3 (0.69)
		Total	1.41 (0.77) b	1.63 (0.99) b	1.36 (0.73) a
	East Europe	Males	1.68 (0.88)	1.88 (1.13)	1.49 (0.81)
		Females	1.53 (0.84)	1.89 (1.13)	1.37 (0.72)
		Total	1.61 (0.87) e	1.89 (1.13) d	1.44 (0.77) b
	Middle East and	Males	1.71 (0.96)	2.03 (1.14)	1.6 (0.94)
	Maghreb
		Females	1.66 (0.97)	2.01 (1.28)	1.62 (1.03)
		Total	1.68 (0.96) f	2.02 (1.2) e	1.61 (0.98) c
	Sub Saharan Africa	Males	2.02 (1.05)	1.87 (1.12)	1.49 (0.84)
		Females	1.85 (1.12)	1.86 (1.15)	1.45 (0.89)
		Total	1.94 (1.08) g	1.86 (1.14) d	1.47 (0.86) b
	Asia	Males	1.57 (0.85)	1.82 (1.05)	1.62 (0.91)
		Females	1.52 (0.94)	1.71 (1.08)	1.54 (0.92)
		Total	1.55 (0.89) d	1.77 (1.07) c	1.58 (0.91) c
	Total	Males	1.6 (0.89)	1.78 (1.03)	1.51 (0.85)
		Females	1.49 (0.84)	1.73 (1.04)	1.41 (0.79)
		Total	1.55 (0.87)	1.76 (1.03)	1.46 (0.82)
	F value (²)	Gender	65.24*** (.003)	9.24* (.0001)	54.24*** (.002)
		Culture	69.64*** (.022)	46.50*** (.017)	36.24*** (.011)
		Interaction	1.92	.752	1.63
	Note.

*  <.05, **  <.01, ***  <.001

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AUTHOR CONTRIBUTIONS

The authors confirm contribution to the paper as follows: study conception and design:

CONFLICT OF INTEREST

The authors do not have any conflict of interest to declare.


Gaël Loubet
email: gael.loubet@laas.fr

Alexandru Takacs
email: alexandru.takacs@laas.fr

Daniela Dragomirescu
email: daniela.dragomirescu@laas.fr

Implementation of a Wireless Sensor Network Designed to Be Embedded in Reinforced Concrete

Keywords: Wireless Power Transmission (WPT), Wireless Sensor Networks (WSN), Cyber-Physical Systems (CPS), Internet of Things (IoT), Simultaneous Wireless Information and Power Transmission (SWIPT), Communicating Materials, Structural Health Monitoring (SHM)

This paper presents the McBIM project (Material communicating with the Building Information Modelling) which aspires to provide a communicating reinforced concretes, thus, addresses the design and an implementation of a wireless sensor network devoted to be embedded in reinforced concrete in order to assure structural health monitoring tasks during its entire lifetime. This wireless sensor network is composed of communicating nodes -collecting, processing and sharing with other communicating materials and with virtual models the generated data, and wirelessly powering and controlling the sensing nodes-and sensing nodes -measuring their internal or environmental parameters, pre-processing and transmitting these to the communicating nodes-. The sensing nodes are battery-free and wirelessly powered by a far-field (radiative) wireless power transmission system. Experiments in the air and from a reinforced concrete beam provide encouraging results.

I. INTRODUCTION

With the rise of technologies dedicated to the Internet of Things (IoT), the Wireless Sensor Networks (WSN) are more and more performant, diversified and common. These last can be used in order to implement Cyber-Physical Systems (CPS) to monitor and/or command some physical objects. This is especially the case for Structural Health Monitoring (SHM) applications, for instance of concrete civil structures [START_REF]IEEE standard for long wavelength wireless network protocol[END_REF][START_REF] Bhuiyan | Towards cyber-physical systems design for structural health monitoring: Hurdles and opportunities[END_REF]. Moreover, and in order to make these systems fully wireless and offer an expanded lifespan, ambient Energy Harvesting (EH) (e.g. photovoltaic, thermal, mechanical, etc.) and Wireless Power Transmission (WPT) solutions are investigated and developed [START_REF] Visser | RF energy harvesting and transport for wireless sensor network applications: Principles and requirements[END_REF][START_REF] Matiko | Review of the application of energy harvesting in buildings[END_REF]. In this context, the McBIM project (Material communicating with the Building Information Modelling (BIM)) -funded by the French National Research Agency (ANR)-tends to propose an implementation of the concept of communicating materials in the construction domain and more specifically by developing a communicating reinforced concrete [START_REF]McBIM research project[END_REF]. This one must be intrinsically able to generate, store -locally and remotely-, process and exchange data -from its own health and/or environment-with other communicating components and with virtual models -as BIM-through the Internet.

Subsequently, the presentation of the McBIM project will be more detailed. Then, the WSN hardware design developed for the implementation of a communicating concrete will be presented, as well as the experimental results achieved to date and providing a full proof-of-concept. Before to conclude, some critical analysis will be proposed in order to explicit current and future works and the contributions of this research.

II. THE MCBIM PROJECT

In order to provide a communicating reinforced concrete linked to an evolutive BIM, a consortium of three French laboratories and one company was set up. Each one has its own role. The LAAS-CNRS (Toulouse) has to implement the hardware part of the communicating reinforced concrete by developing a devoted WSN -this is the purpose of this paper-. The CRAN (Nancy) works on the data collection protocols in the network of communicating reinforced concrete components in order to expend their lifetime by minimizing their energy consumption and need of maintenance, while ensuring their resilience and assuring their scalability [START_REF] Wan | A holonic manufacturing approach applied to communicate concrete: Concept and first development[END_REF]. The LIB (Dijon) trades with the data exchanges and the data integration within BIM platforms by respecting the current standards [START_REF] Roxin | Digital building twins-contributions of the ANR McBIM project[END_REF]. Finally, FINAO SAS/360SmartConnect (Transen-Provence) prospects building and civil engineering companies to get various real-life use cases, as well as providing reinforced concrete elements to do experiments [START_REF]360SmartConnect[END_REF].

The targeted communicating reinforced concrete must meet some constraints. First of all, it must be useful during all its lifecycle: from its manufacture and storage (in the case of precast elements), to its recycling, through the construction of a complete structure based on a combination of elements, as well as the exploitation of this structure, particularly for SHM applications. Thus, its lifespan can be estimated in terms of decades. Then, the communicating reinforced concrete must be scalable in terms of format (e.g. fluid screeds, precast elements for a wall, a bridge deck, etc.) and evolutive during the time in terms of data (type, quantity and periodicity). Indeed, the need in data is function of the step in the lifecycle. For the manufacture, the hourly monitoring of the temperature and humidity evolution during the curing process can help in the decision to continue or not the works (e.g. to unmould a precast element, to tile a floor, etc.). For the storage or the shipping of precast elements and for the construction of a structure, there are the logistic aspects which are the more important, as the ID of elements, their current owner, their location, their delivery address, in which project they must be used, other elements in their neighbourhood, etc. It is also conceivable to create a precise and real-time plan of a structure during its construction, whilst also continuously sharing information between all the stakeholders by using the data stored locally in the element and/or in the BIM. For the exploitation phase, SHM applications are relevant and diverse: the monitoring of temperature and humidity could give information about maturity; the monitoring of the temperature at each side of a wall could be used to quantify its real thermal resistance and certify standards; the cracks detection could allow the application of preventive treatment to avoid irreversible damages and collapses, etc. Thus, with a unique communicating reinforced concrete, different applications can be processed during the entire lifespan of elements by using specific sensors at specific periodicities.

III. DESIGN OF THE WIRELESS SENSOR NETWORK

With the aim of providing a hardware implementation of a communicating reinforced concrete, the choice of the use of a WSN embedded in reinforced concrete for decades was made. In that way, it become possible to render the reinforced concrete intrinsically able to sense its own properties -or these from its environment-, to process, store locally and exchange this data with other communicating materials and with virtual models through the Internet. It also becomes a full CPS.

A. Architecture of the Wireless Sensor Network

The designed WSN -presented in Fig. 1-allows to produce, process, store and exchange data from the physical world to the physical world (e.g. other communicating materials, owner, user or other stakeholder devices, etc.) and to the digital world through the Internet (e.g. BIM, owner, user or other stakeholder information systems, etc.). This WSN is composed of two kinds of smart nodes: the Sensing Nodes (SN) and the Communicating Nodes (CN). The SN make measurements, pre-process the collected data and send them to the CN. The CN collect the data sent by the SN, process and store them. They exchange this data with other CN constituting the WSN and with other WSN, and virtual models -as BIM-through the Internet. They are reachable through the devices of the owners, users or other stakeholders. Finally, the CN can wirelessly supply the SN. Each component of communicating reinforced concrete embed a number of SN and CN function of its size and its needs (e.g. kinds of sensor, desired spatial precision, etc.).

LoRa wireless technology and LoRaWAN protocol in the European ISM 868 MHz band were chosen as communication solution between SN and CN [START_REF]LoRa Alliance technical committee. LoRaWAN 1.1 specification[END_REF]. Indeed, it seemed to be a relatively low energy consumption way to get long range unidirectional communication. Moreover, a wideband signal (through Chirp Spread Spectrum (CSS) technique) seemed less sensitive to the noise induced by the reinforced concrete which appears very binding for electromagnetic waves. Nevertheless, less consuming and medium range technologies as IEEE 802.15.1 Bluetooth Low Energy (BLE) [START_REF][END_REF] or IEEE 1902.1 RuBEE [11] are considered for next developments.

As common ambient energy sources are not usable inside reinforced concrete (i.e. there is no light radiation for photovoltaic, there is locally no sufficient gradient of temperature for thermal solutions, natural vibrations of concrete structure are too low for compact mechanical solutions, ambient radiofrequency (RF) energy is too low for RF EH [START_REF] Matiko | Review of the application of energy harvesting in buildings[END_REF]), the RF WPT seemed to be relevant to have a control way to wirelessly supply the SN by the CN. To have a greater operating distance, the far-field (radiative) solution was preferred to the near-field (inductive) one. Finally, the choice of the European ISM 868 MHz band was driven by a comprised between antenna size and loses in free space.

By using the same frequency band for the wireless communication and power transmission, an implemented and tested solution for Simultaneous Wireless Information and Power Transmission (SWIPT) paradigm is provided [START_REF] Ponnimbaduge Perera | Simultaneous wireless information and power transfer (SWIPT): Recent advances and future challenges[END_REF].

B. Design of the Communicating Nodes

The communicating nodes -presented in Fig. 2-must be able to gather, process and store the data sent by the SN, as well as share these with other CN, other WSN, stakeholders and digital models through the Internet to update them. They are the energy suppliers of the SN through far-field RF WPT. To achieve these tasks, the current CN are composed of a LoRaWAN gateway and a RF power source.

The LoRaWAN gateway embeds a LoRa Server and consists of a Raspberry Pi 3 model B+ micro-computer -with a Linux OS-connected to an IMST iC880A LoRaWAN concentrator for European ISM 868 MHz band. Thanks to software, this one collects, processes and stores the data sent by SN and can access to the Internet and digital world, and be accessed by stakeholders, through an Ethernet or Wi-Fi link.

The RF power source is made of Mini-Circuits components and provides the maximal allowed RF power in the European ISM 868 MHz band of +33 dBm EIRP (or 2 W) [START_REF] Etsi | Electromagnetic compatibility and radio spectrum matters (ERM); short range devices (SRD) intended for operation in the bands 865 MHz to 868 MHz and 915 MHz to 921 MHz; guidelines for the installation and commissioning of radio frequency identification (RFID) equipment at UHF[END_REF]. This one allows to wirelessly power the SN.

C. Design of the Sensing Nodes

The sensing nodes -presented in Fig. 2-must sense some parameters from their internal state or their environment and wirelessly send the measured data to the CN. The SN become inaccessible once deployed in the reinforced concrete, thus, these must be reliable, usable for decades by being energy autonomous and battery-free.

The current SN consist of two parts: one dedicated to the power supply and one to the collect and transmission of data.

For the power supply, a rectenna (for rectifying antenna) developed in our team is used to collected RF power transmitted by the CN and to convert it into electrical power [START_REF] Sidibe | Ultra-compact and high-efficiency rectenna for wireless sensing applications in concrete structure[END_REF]. This dc power is then managed by a Texas Instruments bq25504 Power Management Unit (PMU) which stores it into an AVX BZ01CA223ZSB 22 mF supercapacitor. When enough energy is harvested, the stored energy is used to supply the part dedicated to collect and transmit the data, through a Texas Instruments TPS63031 dc-to-dc buck-boost converter.

For the collect and transmission of the data, a Texas Instruments HDC2010 temperature and humidity sensor achieves the measurement, then the collected data is processed and transmitted by a Murata CMWX1ZZABZ-091 all-in-one LoRaWAN module -which embeds a STMicroelectronics STM32L0 microcontroller and a Semtech SX1276 transceiver-and a meandered monopole antenna.

IV. EXPERIMENTAL RESULTS

To certify the proper functioning of our system, several tests -both qualitative and quantitative-have been carried out.

A. Communicating Nodes

In their current version presented in Fig. 9. C., the communicating nodes are able to receipt the data sent by the SN, as well as process and store it, before make it available to their owner thanks to an Ethernet or Wi-Fi interface, or through the Internet. In addition, they can wirelessly power over several meters many SN located in their neighbourhood.

To provide a Continuous Wave (CW) signal at 868 MHZ with a +33 dBm EIRP power, the RF power source need nearly 4.45 W of power with a 12 V voltage. As well, the LoRaWAN gateway need between 4.0 W and 4.8 W of power with a 5 V voltage to work properly. The amount of needed power is function of its state (standby, processing or reception) and of the connection with other devices (without, through Ethernet or through Wi-Fi). Thus, in the worst case, a 1 Ah battery allows to continuously power the CN for nearly 45 minutes, and a battery of nearly 32 Ah is needed to power it for 24h. In order to release constraints during the development phase, the CN are also accessible and powered by the main supply. Even if the current version of the CN is composed of two distinct sub-systems: the LoRaWAN gateway and the RF power source; with various useful distances in the air: respectively kilometres and meters; these two elements can be located at the same place without communication losses. To go further, preliminary tests with the use of an Aerotek C11-1FFF/OPT.N circulator between a monopole antenna (port 1), the LoRaWAN gateway input (port 2) and the RF power source output (port 3) were successfully performed: a SN at 60 cm and 160 cm from the antenna has be wirelessly powered by the CN and transmitted all its measured data to the CN.

B. Sensing Nodes

In their current version presented in Fig. 9. B., the sensing nodes allow to monitor temperature and humidity of their near environment and to transmit this data once pre-processed over several kilometres thanks to LoRa technology and LoRaWAN protocol. Furthermore, their energy autonomy is assured by a far-field RF WPT technique which wirelessly powers them over several meters. Besides, the periodicity of measurement and communication can be remotely control through the command of the WPT system.

From the SN presented in [15], several improvements were achieved.

First, a more precise temperature and humidity sensor consuming less time (1.6 s instead of 2.13 s for the entire process -measurement and transmission-) and also energy (130 mJ instead of 171 mJ) is used as presented in Fig. 3. Also, by using a dc-to-dc buck-boost converter the energy consumption of the active part is reduced too (by limiting the loses due to higher voltages). Thus, even if the capacity could not have been reduced (22 mF), less energy is needed by the SN (from 214 mJ to 150 mJ) and by reducing the activation (from 5.25 V to 4.45 V) and deactivation (from 2.35 V to 2.30 V) threshold voltages as shown in Fig. 4, less energy is stored (from 245 mJ to 159 mJ, always with extra energy), which allows shorter time for recharge.

What is more, different rectifiers were characterized with the SN. A doubler RF rectifier manufactured on 0.8 mm thick FR4 substrate (Rect1) [START_REF] Sidibe | Ultra-compact and high-efficiency rectenna for wireless sensing applications in concrete structure[END_REF], a compact (1 cm x 2 cm) serial halfwave RF rectifier manufactured on 1.6 mm thick FR4 substrate (Rect2) and a serial half-wave RF rectifier manufactured on 0.8 mm thick Rogers Duroid 5870 substrate (Rect3) [START_REF] Okba | Compact rectennas for ultra-lowpower wireless transmission applications[END_REF] -all based on Schottky diodes-were studied and compared for powering the SN. Fig. 5 shows the times needed for each rectifier to achieve a first charge and recharges (in other words, the times needed to have the first measurement and transmission, and between each next ones), as well as their available output voltage, in function of the available RF input power at 868 MHz. These rectifiers are characterized at 868 MHz which is within a few MHz of their optimum use value. Concerning the output voltages: the Rect1 ones are the highest whatever the input RF power, but the Schottky diodes saturate for powers higher than +6 dBm; and the Rect2 ones are lower than the Rect3 ones, which is justified by the fact that Rect2 was designed with size as a priority and Rect3 with efficiency as priority. Because of this design rule, Rect2 is less efficient than Rect1 and Rect3 with larger first charge and recharge durations. During the cold-start procedure (the main part of the first charge duration), a less than 400 mV voltage is imposed by the PMU, that why Rect3 is faster than Retc1 (which is more efficient for higher voltages) for the first charge. In contrary, when the cold-start procedure is achieved, Rect1 is faster than Rect3 for highest RF input powers, but the two rectifiers are close similar for lowest RF input powers. Regardless of the chosen rectifier, the SN have a periodicity of measurement and transmission which variate between few minutes to hours in function of the available power. Thus, by controlling the RF power source (in terms of transmitted power or duty cycle) it is possible to control wirelessly this periodicity without alter the SN software or hardware parts.

Nevertheless, the energy efficiency of the SN (here defined as the ratio of the energy available at the input of the rectifier (i.e. the integrated available RF input power over the period of interest) to the energy needed for a measurement and transmission) is rather low for the first charge (between 3.4% and 9.2% for Rect1, 2.3% and 7.7% for Rect2 and 4.7% and 9.2% for Rect3) and recharges (between 13.1% and 36.4% for Rect1, 8.3% and 21.7% for Rect2 and 13.1% and 31.0% for Rect3), as shown respectively in Fig. 6 and Fig. 7. As said earlier, Rect3 is more efficient than Rect1 during the first charge whilst this is the opposite during the recharges. For all the rectifiers, the lowest efficiencies during the first charges are for input powers higher than +4 dBm. Only Rect3 sees this efficiency re-increasing for input powers higher than +12 dBm. Moreover, the lowest efficiencies during the recharges are for lowest and highest input powers. To improve this energy efficiency, the electrical losses and the needs in terms of energy must be limited. For instance, the used supercapacitor has losses up to 11.5 µW for a 2.30 V voltage and up to 22.3 µW for a 4.45 V voltage. As well, the needed energy by the SN can be minimized by optimizing the software to shorten process time, by choosing low consumption sensors and transceivers, etc. In this way, the capacity could be reduced, as well as activation and deactivation threshold voltage, and so the losses could be again limited. Also, developing specific and well-defined components could improve the efficiency by reducing the needed energy: for instance, the PMU used needs at least 15 µW just to work. Last but not least, the development of high efficiency rectifier (or RF-to-dc converter) has a large impact on the energy efficiency. In spite of these weak efficiencies, the SN are usable thanks to the data that can be generated and transmitted periodically, nevertheless this criterium has to be take in consideration to provide a sustainable system.

The PCB (14 cm x 9 cm) dedicated to the SN was designed in order to be used as a reflector plan for the rectenna to increase its efficiency and the amount of harvested energy. Even if it was the rectenna presented in [START_REF] Okba | Compact rectennas for ultra-lowpower wireless transmission applications[END_REF] (with Rect3) which was first chosen for the SN, the one presented in [START_REF] Sidibe | Ultra-compact and high-efficiency rectenna for wireless sensing applications in concrete structure[END_REF] (with Rect1) was finally privileged because of a higher efficiency and compactness (from 11 cm x 6 cm x 3 cm to 6 cm x 3.5 cm x 1 cm), despite a lower gain of the antenna (from +6.6 dBi to +5 dBi). This choice will allow to decrease the volume of the SN which is constraint by the antenna and supercapacitor sizes. As presented in Fig. 8, there are good correlations for the duration of the recharges and the output voltage of the rectifier between the SN powered through the rectifier by a controlled RF power and the SN wirelessly powered in the air which scavenges the RF power transmitted by the CN, in the cases of input powers higher than +2 dBm. For lower powers, there are more differences which can be explained by approximations during experiments and in the estimations of the RF power density illuminating the rectenna, but also by the impedance de-adaptation between the rectifier and the antenna which induces an efficiency of the rectenna different than 1, as well as the multipath effects. For these measurements, the SN was located in the air at a distance between 60 cm and 300 cm to the power source and were achieved with a 20 cm step. In spite of these observations, we estimate that the maximal distance between the CN and the SN for the WPT should be higher than 5 meters.

To complement these quantitative tests, several qualitative tests were achieved. A network architecture with a unique CN and multiple SN was tested in the air in order to certify that several SN can be powered by the same CN in a specified area and that the data sent by each SN is well received and processed by the CN. As presented in Fig. 9. A., a SN embedded in a reinforced concrete beam has successfully be wirelessly powered by a CN located 170 cm away to which it sent successfully all the measured data. This 170 cm are composed of 15 cm of reinforced concrete and 155 cm of air. A specific air cavity was designed in the reinforced concrete beam to achieve these tests which are encouraging with the aim of provided a communicating reinforced concrete. Finally, as for the CN, initial tests using an Aerotek C11-1FFF/OPT.N circulator between a monopole antenna (port 1), the rectifier input (port 2) and the LoRaWAN transceiver output (port 3) were successfully achieved: a SN at 60 cm and 160 cm from the CN antenna has be wirelessly powered by it and transmitted it all its measured data. In this way, it is possible to use a unique antenna in the SN and reduce its size.

V. CRITICAL ANALYSIS

Even if some results are encouraging in the purpose of implementing a communicating reinforced concrete, more works must still be performed.

A. Work in Progress

Regarding the sensing nodes, some works are still in progress.

A new version of the SN with an integrated rectifier is being designed in order to get a more compact and more efficient SN. The integration of a RF circulator is under Lastly, first tests of BLE communication -in master/slaves and broadcasters/listener topologies-into the reinforced concrete beam was performed by using NXP QN9080DK development board. Communication distance of 20 meters can be reached with a board embedded in the reinforced concrete beam even if first packet errors appear from nearly 10 meters. It was also possible to achieve lossless communication between two boards embedded in the reinforced concrete beam at a distance of around 90 cm. Nevertheless, there is no evidence to support that communications took place only in the reinforced concrete, maybe another path (through reinforced concrete and air, with a reflection on the ground) has been followed.

B. Perspectives

Some other works are planned or seem relevant to pursuit the McBIM project.

Regarding the communicating nodes, the design and manufacture of a one-part and compact version will allow gains in terms of compactness, energy consumption and efficiency. Also, alternatives to the CW RF power source -as pulses RF power source-are studied with the aim to increase the WPT efficiency and decrease the energy consumption.

Regarding the sensing nodes, other kinds of sensor relevant in the case of SHM of reinforced concrete structures -e.g. strain gauges, corrosion sensors, etc.-are searched in order to be integrated in prototypes. More energy efficient components -e.g. supercapacitor, LoRaWAN transceiver, etcare wanted too. SN prototypes with a BLE communication solution could be interesting in order to have the same order of magnitude between the useful distance of WPT and communication, and to provide a solution needing less energy.

C. Positioning

In order to ensure the energy autonomy of smart nodes, various strategies can be employed as those proposed in the diverse implementations of battery-free LoRaWAN nodes provided in the past years. Some harvest ambient energies (e.g. solar or thermal [START_REF] Lee | Multi-source energy harvesting and storage for floating wireless sensor network nodes with long range communication capability[END_REF], mechanical [START_REF] Orfei | Vibrations powered LoRa sensor: An electromechanical energy harvester working on a real bridge[END_REF], etc.), others are based on backscattering of LoRa signal [START_REF] Talla | Lora backscatter: Enabling the vision of ubiquitous connectivity[END_REF], but although the feasibility of powering LoRaWAN nodes by WPT was demonstrated theoretically in [START_REF] Tjukovs | experimental verification of wireless power transfer ability to sustain the operation of LoRaWAN based wireless sensor node[END_REF], at our best knowledge no full implementation was provided until [15]. By using WPT, the nodes are no more dependent of the availability of ambient energy sources and, by controlling the RF power source, the wireless control of the measurement and transmission periodicity is possible without software or hardware changes.

The majority of the actual wireless and battery-free nodes uses the RFID technologies, which allow short-range communications based on backscattering. These technologies are, for instance, used for SHM applications through active tags [START_REF] Murthy | Batteryless Wireless RFID based embedded sensors for long term monitoring of reinforced concrete structures[END_REF] or tags intrinsically able to quantify a physical parameter [START_REF] Zhang | A review of passive RFID tag antenna-based sensors and systems for structural health monitoring applications[END_REF]. Nevertheless, implementations based on WPT were proposed too, as in [START_REF] Gallucci | An embedded wireless sensor network with wireless power transmission capability for the structural health monitoring of reinforced concrete structures[END_REF] which used short range nearfield (or inductive) WPT and M-BUS medium range communication technology, or in [START_REF] Janhunen | Wireless energy transfer powered wireless sensor node for green IoT: Design, implementation and evaluation[END_REF] which used medium range far-field WPT and BLE medium range communication technology. Equally, solutions based on RF far-field EH were developed, as in [START_REF] Parks | A wireless sensing platform utilizing ambient RF energy[END_REF] but at the cost of a large system. Anyhow, at our best knowledges, it does not exist WSN fully embedded into reinforced concrete and composed of fully wireless sensing nodes wirelessly powered and controlled by a WPT system, dedicated to the SHM of the material during all its lifetime.

VI. CONCLUSION

In this paper, the McBIM project has been introduced, as well as the currently obtained results in its scope. Consequently, a wireless sensor network designed in order to be fully embedded into reinforced concrete able to monitor itself during its entire life has been presented. The first prototypes of smart nodes have been characterized and their tests presented. The communicating nodes, composed of a LoRaWAN gateway and a RF power source, are able to receive, process, store and provide to the final user (through the Internet or a direct link) the data collected and transmitted by the sensing nodes. They are able to wirelessly power these sensing nodes and wirelessly control their periodicity of measurement and transmission through a far-field wireless power transmission system. The fully wireless and batteryfree sensing nodes are, themselves, able to sense temperature and humidity, pre-process the measured data and send them wirelessly -via LoRa technology and LoRaWAN protocol-to the communicating nodes. Several experiments in the air and in a reinforced concrete beam suggest that a unique communicating node could power, control and manage tens to hundreds sensing nodes located in an area of few meters around it. A video presenting the functioning of the CPS system implemented in the reinforced concrete will be presented at the conference. Further experiments will be done for reaching the final implementation of a communicating reinforced concrete.

Fig. 1 .

 1 Fig. 1. Bloc diagram of the architecture of the cyber-physical system composing the communicating reinforced concrete.

Fig. 2 .

 2 Fig. 2. Bloc diagrams of the sensing nodes and communicating nodes.

Fig. 3 .

 3 Fig. 3. Consumption of the sensing nodes with various sensors (SN is powered at 3.3 V from Time = 0.1 s).

Fig. 4 .

 4 Fig. 4. Use of the stored energy by the sensing nodes with a +10 dBm RF power available at the input of the rectifier.

Fig. 5 .

 5 Fig. 5. Durations of the first charge (dashed lines, left) and recharges (dotted lines, left) and rectifier output voltages (dotted and dashed lines, right) as function of the controlled RF power at 868 MHz applied at the input of the rectifier of the sensing nodes for the various rectifiers under test: Rect1 (+), Rect2 (x) and Rect3 (*).

Fig. 6 .

 6 Fig. 6. Energy needed for the first charge (blue) and the energy efficiency of the SN during this first charge (red) as function of the controlled RF power at 868 MHz applied at the input of the rectifier of the sensing nodes for the various rectifiers under test: Rect1 (+), Rect2 (x) and Rect3 (*).

Fig. 7 .

 7 Fig. 7. Energy needed for recharges (blue) and the energy efficiency of the SN during recharges (red) as function of the controlled RF power at 868 MHz applied at the input of the rectifier of the sensing nodes for the various rectifiers under test: Rect1 (+), Rect2 (x) and Rect3 (*).

Fig. 8 .

 8 Fig. 8. Duration of the recharges (blue dotted lines) and rectifier output voltages (red dashed lines) as function of the RF power at 868 MHz at the input of the rectifier of the sensing nodes for the single rectifier Rect1 (+) and the rectenna (*).

Fig. 9 .

 9 Fig. 9. Photograph of (A) the qualitative test achieved with a sensing node embedded into a reinforced concrete beam, (B) the Sensing Node and (C) the Communicating Node.

  consideration in the aim to use a unique antenna in the SN. Works on more efficient rectenna are always pursued too.

This research was funded by the French National Research Agency (ANR) under the McBIM project (Material communicating with the Building Information Modelling), grant number ANR-17-CE10-0014.

ACKNOWLEDGMENT

The authors would like to thank Alassane Sidibe and Dr. Abderrahim Okba from LAAS-CNRS (Toulouse, FRANCE) for developing the rectenna; Philippe Hérail from INSA (Toulouse, FRANCE) for his valuable help during BLE experiments; and all their partners in the McBIM project, especially FINAO SAS/360SmartConnect (Trans-en-Provence, FRANCE) for providing well-defined use cases and a useful concrete beam for experiments.