An Impact study of highway design on casualty and non-casualty traffic accidents.

Background Road Safety has become a worldwide concern due to the alarming repercussions road accidents may bear. This study examined the relationship between different geometric design elements and the accident rates on Rashid Bin Saeed Street, Arabian Gulf Street, and Sultan Bin Zayed Street in Abu Dhabi, United Arab Emirates. Methods The geometric design was collected from the satellite images of google earth in compliance with the standard geometric design manual of Abu Dhabi roads. The recorded geometric data consisted of the number of lanes, lane widths, median length, and width. The traffic volume data was provided by the Integrated Transport Center of Abu Dhabi, which was then converted into Annual Average Daily Traffic (AADT) for analytical purposes. For the studied roads, AADT ranges ranged between 26,509 and 121,890 vehicles per day. The crash data related to the period of 2012-2019 was collected from the online open-access data provided by the United Arab Emirates Ministry of Interior. The data provided had considered variables related to driver gender, age and speed, travel direction, and time of the day amongst other factors. A comprehensive statistical analysis was conducted to study the impact of geometric design elements on road safety through a stable distribution. Stable distributions are generally characterized by four parameters and expressed as X∼S(α,β,σ,μ). The statistical model included several graphical representations such as accident frequency at two levels of severity, casualty and non-casualty accidents for different road segments, traffic volumes, day of the week, age of the injured person, and the geometric design parameters on the three roads. Variance-based methods of sensitivity analysis are also used that are a class of probabilistic approaches that quantify the input and output uncertainties as probability distributions and decompose the output variance into parts attributable to input variables and combinations of variables. The sensitivity of the output to an input variable is therefore measured by the amount of variance in the output caused by that input. Findings The results showed that the accident profiles differ with varying segments on each road, revealing some segments to be of higher accident rates than others. Also, a higher accident frequency was shown with young adult drivers, and a high majority of accidents had occurred on weekends. Regarding the road's geometric design, which is the focus of this study, a sensitivity analysis was made to determine the most influential geometric design element on accident frequency. Interpretation The number of lanes had the highest sensitivity index followed by the median width, and then came the lane width. Thus, modifying the number of lanes on a highway is anticipated to have the highest impact on accident frequency and road safety than any other geometric parameter.