## 2 Literature Review
### Road Geometric and Road Safety
[31] conducted an investigation into the impact of environmental, traffic, intersectional geometric, and pavement-related factors on the total number of collisions occurring at intersections. The study utilized a Poisson model with random parameters to examine collision data collected from 357 signalized intersections located in Chicago during the period spanning from 2004 to 2010. The findings suggest that the examined variables, specifically the standard of pavement, unilluminated intersections, and the quantity of traffic during the evening rush hour, exert the most notable influence on the frequency of collisions. The results indicate that it is crucial to prioritize the adequatemaintenance of pavements and appropriate illumination of intersections to effectively promote safety measures pertaining to highways at intersections. [PERSON] and [PERSON] [66] demonstrated the relation by analyzing accidents at 120 intersections in Adelaide, Australia. Among more than five million hourly measurements, a dataset of 1629 accidents involving motorized vehicles was discovered. The effects of rainfall were also studied. The correlation between accident frequency and traffic volume was essentially linear for lower traffic volumes, according to the findings. Poisson and negative binomial models exhibited a robust quadratic explanatory component as accident frequency increased at a faster rate with increasing traffic volume. In Abu Dhabi, [PERSON] at al. [61] carried out a study using a negative binomial regression model. The study aimed to identify the influence of geometric design conditions, such as the number of lanes in three-leg, four-leg, and other intersection types, on severe accidents, red light violations, safety performance indicators, and property damage. The study indicates that most accidents and traffic light violations take place at intersections with three or four legs where minor streets intersect. Expanding the number of lanes on the minor streets could be a potential solution to this issue, which would effectively transform them into major streets. In order to ascertain the correlation between road alignment, road geometry, traffic conditions, and crash frequency, [PERSON] et al. [67] developed accident prediction models for two-lane rural horizontal curve segments. According to the research, lane width is more crucial than traffic volume, curve radius, and curve type in determining accident frequency. [PERSON] et al. [68] also discovered these issues with accident severity by using databases from the public works and police departments, which contained 1067 cases of varying degrees of severity recorded on Malaysian roads between 2008 and 2015. Nine different variables were examined and developed into an ordered regression model for the severity of accidents using these records. The findings showed that poor horizontal alignment had an impact on the model's predictions. In comparison to the absence of such factors, the probability of a more severe accident caused by bad horizontal alignment was correspondingly about 0.4 times lower. The combination of a horizontal curve and a gentle slope on a mountain highway increases safety, whereas combinations of a horizontal curve and a steep slope or a vertical curve and a horizontal curve increase the risk of an accident. When the concave vertical curve and horizontal curve are combined, the risk is marginally lower than when horizontal curves and convex vertical curves are combined. In mountainous areas, it is advantageous to control vertical slopes and lessen the intersection of vertical curves and horizontal vertical curves [69]. The Intersection is the most prevalent location for vehicle accidents. Intersections on single-level highways are among the most hazardous locations for vehicle accidents [PERSON] at al. [61].