# Impact of Putting on Traffic Safety: A Synthesis of Research Findings
## 3 Results and Discussion
### Weather Conditions
However, several studies have reported a limited impact of rut depth under both wet and dry conditions. [PERSON] et al. [45] reported a limited effect of rut depth on the crash risk in wet and dry conditions. The crash rate was found to increase by less than 5% when the RD increased from 0 to about 20 mm. However, a slight reduction in the accident rate was reported on the further increase in the rut depth. [PERSON] and [PERSON] [25] stated that both dry and wet pavement have minimal impact on driving safety. Driving Trajectory (Path Changing and Straight Line)  
The impact of driving trajectory was explored in a limited number of studies. Some field observation studies hinted at the increased risk of rutting when drivers try to exit or enter the rut grooves. For instance, [PERSON] et al. [10] reported an accident caused by control loss while exiting a rut on pavements. Although seemingly intuitive, there is insufficient analysis to conclusively determine the significance of the driving path's influence on the impact of rutting on traffic safety, primarily due to the lack of detailed data in accident databases. However, multiple simulation studies have considered the impact of rutting on driving stability when changing the path compared to driving on the same path [29; 51]. Rutting was found to be more dangerous when intersecting ruts compared to driving along the ruts [29; 51]. Therefore, prioritizing the management of rutting on multi-lane roads where lane changes are anticipated is essential. The type of road is expected to influence the impact of rutting due to variations in AADT and speeds. However, there is a lack of comprehensive evidence on how different road types affect the relationship between rutting and traffic safety. Existing studies comparing various road types generally report minimal or even positive impacts of rutting on traffic safety. [PERSON] and [PERSON] [43] observed differences in the impact of rutting on traffic safety between urban and rural roads. In urban roads, accident rates decreased significantly at rut depths greater than 10 mm, in contrast to fluctuations observed on rural roads. [PERSON] et al. [20] reported a statistically insignificant impact of average rut depth on traffic safety across three highway classes. The same study found that maximum rut depth was statistically insignificant for two highway classes and marginally significant for the other. The averaging of rut depth over large segments is thought to minimize the statistical significance between rut depth and accident rate. Speed  
Although rutting is expected to impose a higher accident risk on higher-speed roads, the limited field observation studies do not provide sufficient evidence to support this notion. Table 4 summarizes the results reported by [PERSON] et al. [13] on the impact of rutting at different speeds and AADT across different Nordic countries. In the data analyzed for Sweden, Finland, and Norway, rutting was reported to have a minimal or positive impact on traffic safety. However, the results vary across different AADT and speed classes and are inconsistent with those of adjacent classes, making the findings difficult to interpret and less useful for establishing maintenance guidelines. In contrast, simulation studies clearly show a critical impact of speed on the risk imposed by rutting [26; 27; 28; 30; 33; 35; 37; 38; 39; 51]. Furthermore, multiple studies have emphasized the importance of limiting the speed on roads with higher rut depths, particularly in rainy weather [35; 37].