The Impact of Combined Weather Factors on Traffic Flow Parameters in the Irish National Road Network

Transportation infrastructure is increasingly exposed to and affected by adverse weather conditions. These conditions significantly impact everyday human decisions and activities. To alleviate the degree of impact, engineers have sought to incorporate weather-related data into traffic operations and procedures. Understanding the relationship between weather and road performance will allow infrastructure stakeholders to improve network resilience and refine operating strategies. However, before incorporating weather information into traffic and road guidelines, there is a need to quantify the impact of varied weather factors on road performance. Inclement weather does not only affect main roads, such as highways and freeways. It also
drastically reduces the performance of primary and secondary road networks. This paper investigates the impact of inclement weather on traffic volume and speed across varied primary and secondary road networks in Ireland using historical traffic and weather data. The study provides an insight into the independent and combined effects of temperature and rainfall on traffic performance in Ireland. The intensity of the weather factors is vital to the investigation. As such, varied rainfall intensities (light, low-moderate, high-moderate) and temperature ranges (optimal, low) are considered for each road under investigation. The results indicate that the combined effect of low temperature and rainfall contributes to the most significant reductions in traffic speeds and volume across primary and secondary road networks.