A notable finding of this study was that although the rate of injuries was significantly higher in Anzali and Rasht, accidents occurring in foggy condition caused huge damages and injuries in most of the cities. A study of all areas of the United States except Northwest and New England reported similar results (25). In an Iranian three-year study on the Firouzkooh-Sari road, 930 road crashes were identified over a distance of 131 kilometers. The highest risk of fatal accidents belonged to the distance of 98, 100, 106, 109 and 110 kilometers, and due to the installation of fog lights at 9 to 18 kilometers (before and after the mountain pass or road curve), these types of accidents were prevented to a huge extent (26). Therefore, it is likely that the differences in the magnitude and severity of accidents be due to the installation of lighting and fog lights and other road facilities in different cities of Guilan with varying numbers and qualities.
According to the results of the present study, the mortality rate due to RTAs decreased significantly with age. In fact, this type of accidents in northern Iran follows a specific age pattern in terms of rate of mortality of drivers. In a similar research which scrutinized the relationship between all certain weather conditions including rain, fog, dust, etc. and traffic accidents, significantly less number of RTAs were observed in older drivers (40–60) (27). There are various reports insisting that older drivers may be at greater risk of injury due to the reduced ability to detect impending events and fail to maintain a safe headway distance (14). If we assume age and experience as two similar concepts, a study reported that more experienced drivers compared with novice drivers were significantly less likely to lower their speed (17). Experienced drivers are also less likely to approach the front vehicle than novice drivers, which gives them enough time to respond appropriately (14). However, these differences may be related to the different age range included in each study.
The pattern of RTAs in the foggy condition was significantly associated with the male sex. That is, men were more likely to have accident than women in such condition, however, the likelihood of death dramatically increased in accidents where a female driver was at-fault. In a similar study, female drivers were more likely to deviate from the straight path in fog and involved in a single-vehicle accident in dense fog. It is noteworthy that male drivers usually drive at high speeds in foggy conditions since they usually have more confidence in their driving skills than female drivers (28). But in a study in Pakistan's urban areas, men were more likely to be involved in traffic accidents than women in all types of weather (27). Also, according to a logistic model, sex was the only characteristic associated with the deceleration of the vehicle in foggy weather. Evidence suggests that the average speed of women is more affected by fog than men at speeds of up to 10 mph. This means that women are probably more cautious when driving in foggy conditions and have a more responsible attitude than men because male drivers are more likely to risk speeding when the immediate dangers are unclear (29, 30). Still, more detailed studies are required.
In the present study, there were no significant differences in the number of injuries in foggy weather compared with other conditions, but the mortality rate was significantly higher than other climatic conditions. In one Iranian study, however, the number of accidents in rainy weather (73.8%) which led to damages was higher than the number of accidents leading to death, which was due to the slower speed of vehicles in such conditions compared with sunny weather (31). In a time series analysis in northern Iran, the first day of rainfall after several dry periods was significantly associated with morbidities and mortalities due to accidents (32). This may imply that fatal accidents in fog are so severe that they lead to immediate death because of the severity of the injuries.
Most of the fatal accidents related to foggy weather occurred in the autumn (November) and winter (January and February) whereas the number of these accidents was significantly lower in warm months including June, July, August and September. A study on accidents in the USA in cold weather in winter season published similar findings according to which the highest rate of deaths due to RTAs dedicated to cold days of winter (33). Furthermore, Abdel-Atyet al. (2011), found similar results where the highest number of accidents had been recorded for smog weather occurring during winter (34). According to the data obtained from the FARS database, 40% of fatalities occurred in fog, smoke, dust storm and sand storm, with most of them occurring in December, March, and April (35). In an Iranian study, dense fog (less than 40 meter vision sight) was highest in February (31). Therefore, in the present study, the pattern of RTAs in the fog had a seasonal pattern and had a significant increase in winter compared with summer. However, previous studies have reported that drivers tend to go faster in clean weather due to good visibility so they usually speed up in clear weather in foggy weather (1, 5). Although the dense fog is often observed during the winter when the average speed of vehicles is slower and the number of tourists is remarkably lower than that of other times of the year (36), the number of accidents under foggy weather is surprisingly high which needs more investigations.
Studying the mortality rate of RTAs in foggy weather at different hours of the day in Guilan province from 2014 to 2018 revealed that the mortality rate significantly decreased at 2 AM, 11 PM, 13 PM and 19 PM. The number of injuries decreased dramatically at 2 AM, 3 AM and 2 PM. In the study by Black and Mote (2015), the highest number of fatalities in fog due to RTAs belonged to evening time (33), and in another study, the most frequent fatalities were in smog condition in the morning in winter (34). However, due to the lack of available data related to certain times of the day/night, an accurate analysis was not possible.
Examining the mortality and injury rates of RTAs in the fog revealed that the incidence of these accidents did not change significantly in Guilan from 2014 to 2018. Thus, it can be concluded that with advances in knowledge, technology and resource development, etc., there has been no reduction in these types of accidents within this time and there is a need for more effort to prevent such accidents. However, it should be noted that atmospheric phenomena can only exacerbate the cause of accidents and they should not be accounted for as the mere causes of these events. A study on bad weather conditions (snow, ice, rain, and fog) in Iran specified that these conditions caused a total increase in the risk of accidents by 6.6% (26).
Although natural phenomena such as fog, snow, cold weather, etc. cannot be prevented, some variables can be interfered with. For example, the driver's information on safe driving in such weather conditions can be improved by installation of not only the common road warning signs but also some signs containing brief messages about driving skills in foggy weather in hot spots with a higher likelihood of fog (37).
One of the limitations of this study was that the information obtained from traffic police about several variables such as the hour of accidents leading to mortality or morbidity and the city where accidents took place were incomplete. Moreover, the accidents which involved animals or hitting a traffic sign and the accidents not being reported by the driver were excluded from the study. Therefore, the number of recorded accidents may not showcase the actual number of accidents (under-report). However, our findings were similar to those of related conducted studies in other countries.