# Bayesian Modeling of Traffic Accident Rates in Poland Based on Weather Conditions
## 1 Introduction  
Road Traffic Accidents (RTAs) represent a major global public health concern, resulting in approximately 1.19 million deaths annually and leaving between 20 and 50 million people with non-fatal injuries [1]. In addition to the human toll, RTAs impose substantial economic burdens, with estimated costs ranging from 1% to 3% of national GDPs [2]. World leaders understand this issue, and so the United Nations General Assembly proclaimed the decade 2021-2030 as the Second Decade of Action for Road Safety, aiming to reduce road traffic deaths and injuries by at least 50 percent [3]. Similar resolutions have been adopted by the WHO [4] and the European Commission [5], among many others. In recent years, Poland has emerged as a leader in road safety improvement within the European Union, achieving a staggering 44% reduction in road accident fatalities between 2013 and 2023 [6]. However, despite these gains, traffic accidents continue to pose substantial societal and economic burdens. According to the Polish Road Safety Observatory, Poland recorded over 21,000 traffic accidents in 2024, resulting in nearly 1900 fatalities and more than 24,000 injuries [7]. Systematic solutions to lower the number of RTAs are needed, but without understanding the underlying causes it is infeasible to eliminate their tragic outcomes. The complex nature of traffic accidents stems from the interplay of diverse factors, involving traffic conditions, human factors, vehicle design and condition, infrastructure characteristics, and environmental variables [8]. Among these, traffic exposure represents the most fundamental one, suggesting that minimizing traffic volume would be the most effective way to reduce the number of accidents [9]. However, since traffic reduction is rarely feasible, other contributing factors must be carefully analyzed. Vehicle speed plays a critical role in road safety, affecting both the risk and severity of crashes [10; 11]. Human factors substantially influence accident risk, with both fatigue and distraction emerging as key concerns [12]. Driver distractions span numerous categories, including mobile phone use, navigation system interactions, passenger conversations, audio system adjustments, and in-vehicle dining [13]. Fatigue degrades driving performance progressively with extended driving duration, with monotonous driving environments further contributing to decreased driver alertness [14]. Vehicle-related factors encompass both technological advancements and maintenance issues. Advanced safety systems such as Forward Collision Warning (FCW) and Autonomous Emergency Braking (AEB) have demonstrated remarkable effectiveness, contributing to the reduction of front-to-rear crashes and associated injuries [15]. Beyond technology, inadequate maintenance, such as insufficient tire tread depth, affect accident rates in a meaningful way, particularly on wet road surfaces [16]. Road infrastructure plays a critical role in both accident prevention and mitigation. Thoughtfully designed pedestrian infrastructure--including refuge islands and signalized crossings--can substantially reduce pedestrian-related accidents [17]. The concept of \"forgiving\" road infrastructure suggests that well-designed roads can help mitigate the consequences of driver errors [18]. Numerous studies have established a clear link between adverse weather conditions and increased crash frequency and severity, highlighting the importance of analyzing this relationship [19]. The impact of precipitation demonstrates temporal nuances, as rainfall following extended dry periods presents heightened hazards [20], while snow days have fewer fatal crashes than dry days, but more nonfatal-injury crashes [21]. Low friction on snow- and ice-covered roads amplifies collision risk, underscoring the importance of road maintenance in adverse conditions [22].