Roads Accidents Affected by Weather Conditions

Introduction and Background

Despite the strict regulatory policies established to protect drivers’ and pedestrians’ safety, road crashes are still a major cause of concern in the United Kingdom. In 2014, the lowest year on record, over 1700 people died in car accidents in the United Kingdom (International Transport Forum 508). Among the factors which contribute to the likelihood of road accidents are unfavorable weather conditions.

Weather-related road accidents are such accidents which occur in the presence of unfavorable weather conditions, or such conditions that make driving more difficult (Pisano, Goodwin and Rossetti 1). Such weather conditions include rain, fog, sleet, and others. The number of fatalities linked to road accidents has been shown to correlate with weather conditions. A study done in the cities of Calgary and Edmonton, Canada showed that road accident risk is 70% higher in unfavorable weather conditions (Andrey and Yagar 465).

In the United Kingdom, adverse weather conditions pose a risk to the drivers’, and pedestrians’ safety. Statistically significant annual fluctuations have been observed corresponding to changes in weather conditions in the United Kingdom between 2005 and 2014 (International Transport Forum 176). This data prompts researchers to evaluate driving behavior and vehicle performance concerning adverse weather conditions and the way unfavorable weather affects crash risks. Such research is necessary to establish regulatory policies which can help minimize the likelihood of road accidents in unfavorable weather conditions.

Weather conditions affect driving behavior in several ways. Vehicle performance can become compromised on wet roads, in strong winds, and extreme temperatures. Drivers’ capacity is also limited as the result of impaired visibility in heavy snow, rain, and fog (Pisano, Goodwin, and Rossetti 1). In unfavorable weather conditions, road surface friction may be lower, requiring drivers to reduce speed and keep a safe distance to the car driving ahead to avoid accidents. In addition to lower friction, tailgating, or the process of driving too closely behind another vehicle, becomes a dangerous risk.

Driving too close from the vehicle in one’s front results in a very high percentage of traffic accidents on the road, the majority of which are rear-ended collisions. In China, for example, tailgating accounts for approximately 16% of all the recorded road traffic accidents (Duan and Li 25). The headway, or the measurement of time or distance between two vehicles in a single lane, is founded on the response time of motorists and takes into account vehicle performance. While both the driving capacity of motorists and vehicle performance are compromised in unfavorable weather, shorter headways might result in higher crash rates.

Research Aim

This paper seeks to assess the strong link between road accidents and adverse weather conditions such as high temperatures, high atmospheric pressure, and heavy rainfall, among others. The findings of a case study, performed in Greater Manchester, UK, are analyzed, with the focus on spot speed and headway time and distance concerning road accidents in adverse weather conditions. With the inclusion of several statistics on these road accidents, the researcher attempts to raise awareness among the people of the United Kingdom.

Research Objective

The research objectives are very useful to generate in-depth insights on the research topic which can enhance the research’s analysis. To divide this broad research topic into small but appropriate forms, the establishment of research objectives is necessary. The researcher has framed some relevant research objectives based on the research aims for the proper categorization of the research topic in an appropriate form. These include:

  • to critically assess the findings of the case study performed in Greater Manchester, UK, with the focus on spot speed and headway time and distance concerning road accidents in adverse weather conditions;
  • to provide recommendations on weather-related road accidents mitigation strategies;
  • to raise awareness about the issue of adverse weather conditions and the effect they have on road accidents;

Case Study Methodology

The researcher used an observation method for data collection. The survey was conducted in Albion way in Salford, Greater Manchester. Data was collected by a camera and a radar gun in peak hours in favorable (dry weather) and unfavorable (rainy weather) weather conditions. The total recording time was over one hour.

Only one lane was taken into consideration. Data were not included in those cases when radar measurements could be compromised. Such cases included vehicles in parallel lane driving close to the vehicles in the observed lane. The data from a total of 135 vehicles were taken into account when preparing the case study based on the fact that there was no presence of a platoon of vehicles on the opposite lane.

A free flow speed survey was also conducted with the use of a speed gun during wet and dry weather conditions so that the changes in the average speed maintained in each situation could be observed. A free flow speed survey was conducted with the use of a speed gun at the same spot at the curve in Albion’s way. Also, the same survey was undertaken in dry and wet weather conditions while the first vehicle’s speed was detected in each platoon to see to it that the conditions of all the speed are free to flow.

A standard for the measurement of the headway distance was a selected sign of the road. The computations of the vehicle’s headways were computed when the bumper on the vehicle began approaching the sign. The vehicle headways were highlighted by the time interval between two vehicles that are behind one another upon reaching the defined standard.

The Analysis of the Findings

Spot Speed Data in Favourable (Dry) and Unfavourable (Rainy) Weather Conditions

The speed limit of the observed road is 40 Mph. Speed percentiles included in the analysis are the 50th and the 85th percentiles. The 50th percentile represents the median and average speed of the traffic. 50th percentile implies that half of the cars are driving below that speed, and half of them are driving above that speed. The 85th percentile is usually utilized as a guide in instituting speed limit since 85% of drivers drive below this speed and consider it safe. In other words, the 85th percentile can be viewed as the highest speed deemed safe by the drivers. Minimum and maximum observed speeds were also included in the analysis.

Throughout the observation, it was discovered that in favorable (dry) weather conditions, the average speed of the cars was 31 Mph and a standard deviation was 4.3 Mph. The speed mode was discovered to be 30 Mph while the 30 Mph was the median. The 85th percentile vehicle speeds and the 50th percentile vehicle speeds are 34 Mph and 28.5 Mph respectively. The observed maximum speed was 52.5 Mph while the observed minimum speed was 16.5 Mph.

Throughout the observation, it was discovered that in unfavorable (rainy) weather conditions, the average speed of the cars was 31 Mph and a standard deviation was 4.4 Mph. The speed mode was discovered to be 30 Mph while the 30 Mph was the median. The 50th and 85th distribution percentiles were 28.5 Mph and 34 Mph for the speeds of the vehicles on 28.5 Mph and 34 Mph respectively. The observed maximum speed was placed at 52.5 Mph while the observed minimum speed was 16.5 Mph.

The findings of the spot speed observation data show that spot speed data is identical in the two types of favorable and unfavorable weather conditions examined. This data shows that in at least this particular road section, speed percentiles are not affected by wet or dry road surface conditions. This has several implications for the topic of the paper.

Speed is a perilous aspect of all highway crashes and fatalities. Driving is volatile, and if something unpredicted occurs on the road it is a motorist’s speed that will predict whether they can hit the brakes in time and if they can’t dodge the accident, how grave will it be. Consequently, lowering and handling traffic flow speeds is central to road security.

The data of the case study shows that speed reduction is not associated with dry and wet surface conditions alone. Previous studies suggest that the combination of low visibility, heavy winds, and/or heavy precipitation (such as heavy snow) typically results in a 30-40% reduction of traffic speed (Cao et. al. 2).

As such, it can be concluded that drivers adjust their driving speed based on visible environmental factors, such as low visibility, heavy winds, etc., and rainy weather alone does not prompt drivers to reduce speeds if no other factors are present. Since the unfavorable weather did not limit visibility, the drivers were reluctant to reduce their speed. Wallman and Astrom argue that drivers decide to reduce speeds mainly based on the appearance of the surrounding environment (5). The result of the spot speed observation suggests this is true.

However, same-looking environments may pose a different challenge to the driver (Wallman and Astrom 5). This is the result of road surface slipperiness and tire-road friction. While rainy weather alone does not affect the speed of traffic in the observed section of Albion way in Salford, rainy weather does result in road slipperiness which compromises vehicle performance.

Road slipperiness is measured either through tire-road friction or braking distance. Friction is “the resistance an object encounters in moving over another object” (Wallman and Astrom 8). On wet rough surfaces, such as the road surface, “rubber friction […] is typically 20 − 30% smaller than for the corresponding dry surfaces” (Persson et. al. 1). Lower friction results in longer braking distance, which is the distance the vehicle travels until full stop. During the winter season, road surface may be covered with snow or ice, which lowers friction even further. As such, road friction is one of the major factors which affect road safety.

“Maintaining a certain safety level demands that driver adapts their behaviour to changing friction conditions, mainly by adjusting their speed” (Wallman and Astrom 26). Adverse weather conditions require drivers to be attentive at all times and use visual, auditory, and kinetic feedback to adjust their speed. In particular, this information should be used by the drivers to estimate the level of friction. Ideally, if the tire-road friction is considered by the driver, the driver will adjust the speed to compensate for lower friction and will stop at the same distance.

However, the motorists’ perception of the level of friction is generally poor (Wallman and Astrom 26). The data gathered during the case study suggests it is true. Even though the surface of the road was wet and friction was lower, the speed of the traffic was identical to that on the day when the weather was dry. Because the speed is not reduced to the required level, the likelihood of road accidents is higher in rainy weather.

Scientific evidence was gathered in support of poor stopping adaptation in different countries around the globe (Wallman and Astrom 27). Poor stopping adaptation poses an even greater risk if headway distance is not enough to compensate for longer braking distance. The headway data is the focus of the next section.

The Headway Measurements in Favourable (Dry) and Unfavourable (Rainy) Weather Conditions

Safe headway is dependent upon various conditions, including the vehicle’s speed breaking capacity and visibility level. Both the vehicle’s speed breaking capacity and visibility level are connected with weather conditions. In unfavorable weather conditions, such as rainy or snowy weather, the vehicle’s breaking capacity is affected by reduced tire-road friction. Additional environmental factors, such as low visibility due to fog, also require the driver to keep longer headway distance. Longer headway distances allow divers to prevent rear-end collisions in case of emergency braking. At the same time, shorter headway may result in a higher percentage of accidents.

Throughout the observation, it was discovered that in unfavorable (wet) weather conditions, the average time headway with 0.01 seconds accuracy was 3.08 seconds. For wet weather conditions, the lowest average headway was calculated for vehicles driving at the lowest speeds of 12-14 Mph and was 2.32 seconds. The highest average headway, 4.22 seconds, was calculated for vehicles driving at the highest speeds of 26-28 Mph. For the majority of vehicles, however, there was no correlation between speed and time headway averages. While certain vehicles were driving at higher speeds, their time headway was roughly the same as that of the vehicles driving at lower speeds.

As for dry weather conditions, the average time headway with 0.01 seconds accuracy was 3.06 seconds. Vehicles driving at the lowest speeds of 12-14 Mph had higher average headway time, 3.14 seconds than the majority of vehicles driving at higher speeds. Again, the highest headway, 4.15 seconds, was calculated for vehicles driving at the highest speeds 26-28 Mph. For the majority of vehicles, however, there was no correlation between speed and time headway averages.

The findings of the case study suggest that drivers on the observed section of the road do not adjust time headways based on weather conditions. The average time headway was almost identical for both dry and wet weather, and the 0.02 seconds difference is too small to have any statistical significance. The findings show that drivers do not consider road slipperiness.

Drivers are found to be poor at evaluating the level of road slipperiness and therefore, fail to produce accurate measurements of stopping distances. The findings correlate with spot speed data and previous research. The research performed by the Finnish National Road Administration showed that only one-third of the drivers were able to correctly measure road slipperiness (Wallman and Astrom 28). Even though the surface of the road in wet weather increases braking distance two-fold, the average headway times were identical for favorable and unfavorable weather conditions. Because headway time did not increase in wet weather, the likelihood of rear-end collisions is higher in rainy weather.

Recommendations on Road Accidents Mitigation Strategies

To reduce the negative impact of unfavorable weather conditions on road accidents, it is important to use a complex approach. Several strategies are proposed to improve road safety in areas with adverse weather conditions:

  • Providing relevant information to drivers. This strategy includes raising awareness about the negative impacts of negative weather conditions on road accidents and providing drivers with road weather information through different warning systems. Raising awareness can be done through advertising and social media campaigns. Dissimilation of information about unfavorable weather can be done through mobile networks, TV, radio, or the Internet. Government agencies should provide timely information to prevent accidents.
  • Administrative regulation. This strategy implies establishing relevant regulatory policies to improve speed management in unfavorable weather conditions. Also, in case of severe disruption, certain road sections should be closed for drivers’ safety. Through control, government agencies can prevent road accidents due to dangerous weather.
  • Proper road and infrastructure design. This strategy requires building roads with sufficient texture which allows the tires better grip onto them. Also, it requires restricting the usage of chemicals which leads to increased slipperiness. Certain actions have to be taken to improve friction in wet or snowy conditions, such as providing sufficient drainage or removing snow or ice from roads. De-icing operations require establishing organizations that will collect the data on road slipperiness and initiate chemical frost removal.

Conclusions

Driving a car is a highly complex task, more so in unfavorable weather conditions. Weather-related road accidents are such accidents that occur in the presence of unfavorable weather conditions. The adverse climate of the United Kingdom means that careful management is required to minimize the occurrence of weather-related road accidents. In many parts of the United Kingdom, rain occurs year-round and increases the chances of road accidents due to slippery roads and impaired visibility.

The results of the case study show that drivers contribute to the problem by their inability to adequately reduce driving speeds or increase headway time in wet conditions. Previous research also suggests that drivers are generally not able to avoid weather-related accidents by themselves and are poor at evaluating road conditions.

While many factors contribute to the likelihood of road accidents, unfavorable weather conditions are easy to avoid if regulatory action is taken to reduce the effect of adverse weather conditions. The governmental effort should be three-fold and aim to improve speed management, protect roads from adverse weather, and establish weather-related warning systems. It is important not to underestimate the effects weather-related accidents have on the day-to-day life of the country.

Works Cited

Andrey, J. and S. Yagar. “A temporal analysis of rain-related crash risk.” Accident Analysis & Prevention. 25.4 (1993): 465-472.

Cao, Luchao, Lalita Thakali, Liping, Fu, and Garett, Donaher. 2013. Effect of Weather and Road Surface Conditions on Traffic Speed of Rural Highways.

Duan, Jiyang and Zhizhong Li. “Risk illusions in car following: Is a smaller headway always perceived as more dangerous?” Safety Science. 43 (2013): 25-33. Web. 26 Aug. 2016.

International Transport Forum. Road Safety Annual Report 2016, Paris: OECD Publishing. Print.

Pisano, Paul, Lynetter, Goodwin and Michael Rossetti. U.S. Highway Crashes in Adverse Road Weather Conditions.

Wallman, Carl-Gustaf & Astrom, Henrik. 2001. Friction measurement methods and the correlation between road friction and traffic safety. A literature review.