Exploring regional differences in cyclist safety at roundabouts: A comparative study between the UK (based on Northumbria data) and Belgium.

The level of safety for cyclists at roundabouts may vary according to national differences not only in the design itself but also sociodemographic, cyclist and driver behaviour as well as environmental factors. This paper investigates the national influence on cyclist casualty severity at roundabouts by comparing the United Kingdom (using Northumbria as a representative sample) and Belgium. The data included speed limits, socio-demographic characteristics, environmental conditions and driver/cyclist behaviour-related contributory factors. First, a logistic regression analysis for the UK data, including 864 cyclist casualties, was carried out. Increasing the speed limit by ten units (for example 30mph to 40mph) increased the probability of a cyclist being killed or seriously injured by 10%. A cyclist casualty was more than three times more likely to be killed or seriously injured (the odds ratio is 3.02) where sudden braking was recorded as a contributory factor. Second, a separate logistic regression analysis for Belgium was conducted. Cyclists ignoring the priority at roundabouts increased the probability of a fatal or seriously injured collisions (the odds ratio is 2.71). Comparing the individual analysis for both countries, the influence of cyclist age was consistent. Each one-year increase in cyclist age increases chance of being killed or seriously injured as opposed to not being killed or seriously injured by 2 % (odds ratio is 1.02) in both UK and Belgium. A final comparative analysis was applied considering proxy variables for both countries. Three-way chi-square tests of independence showed that all non-behavioural variables (i.e. sociodemographic characteristics, speed limit, and environmental conditions) were found to be statistically different between UK and Belgium for both slight and killed and seriously injured casualties. This suggests that driver/cyclist interaction and behaviour in the two countries is generally similar whilst speed limits, the sociodemographic characteristics of cyclists and environmental conditions are specific for each country. The third part of the logistic regression analysis suggested that the country residual was highly statistically significant. This indicates that there are some statistically significant differences with respect to the characteristics of the two regional datasets used in the analysis.

Cyclist casualty severity at roundabouts - To what extent do the geometric characteristics of roundabouts play a part?

INTRODUCTION: In general, priority junctions are converted into roundabouts to increase capacity and reduce vehicle accidents. However, previous research has indicated that roundabouts are dangerous for vulnerable users, especially cyclists. METHOD: This paper investigates which design factors influence cyclist casualty severity at give way (non-signalized) roundabouts with mixed traffic, using the UK STATS19 National dataset of cyclist casualties. First, the correlation matrix was generated to observe the relationship between variables. Second, dimension reduction was applied to geometric design variables in order to reduce the number of variables and generate the factors. Finally, the binary logistic regression method, with serious and slight casualties as dependent variables, was applied in three steps. The first Binary Logistic Regression Model (BLRM) included speed limit, sociodemographic, and meteorological conditions. The variables in the second BLRM consisted of geometric design variables. The third BLRM included the factors that were generated by dimension reduction. RESULTS: The correlation matrix revealed that the number of lanes on approach and half width on approach were statistically significantly correlated, while the variables, such as geometric design (entry path radius, number of arms, number of flare lanes on approach, type of roundabout and number of circulating lanes), sociodemographic (casualty gender and age), speed limit and meteorologically related factors (daylight, weather and road surface condition), did not show any statistical significance. From the dimension reduction process, two main factors were identified, including Approach Capacity (Factor 1) and Size of Roundabout (Factor 2), and they were subsequently used as independent variables in the logistic regression analysis. The subsequent BLRMs showed that a higher speed limit reduces the safety for cyclists at roundabouts. The probability of a serious casualty increases by approximately five times (odds ratio 4.97) for each additional number of lanes on approach and by 4% (odds ratio 1.04) with a higher entry path radius. It was also found that Factor 2 (Approach Capacity) increases the casualty severity (odds ratio 1.86) for cyclists at roundabouts. Practical applications: While this research studied roundabouts in the UK, the methodological approach and statistical analysis techniques are applicable to other countries and the findings are likely to be of value to decision makers worldwide.