Influence of Vegetation Density on Vehicle Speed and Position of Roadway

Abstract

According to the World Health Organization (WHO), over 1.2 million people lose their lives each year in motor vehicle crashes and disable millions of people annually around the world. Based on crash data in the United States, single-vehicle collisions with trees account for nearly 25% of all fixed object crashes each year, resulting in deaths of approximately 3,000 people and making up approximately 48% of fixed-object fatalities. The injuries and fatalities due to single vehicle-collisions are a significant component of road crashes in Sri Lanka. The objective of the study was to evaluate the drivers’ speed selection and lateral position of vehicle from the presence of roadside elements within proximity to the roadway. Parameters affecting drivers’ speed and lateral positioning of the vehicles on the road were chosen based on literature review. Random vehicles in each selected location were observed and the information on all the parameters were collected which identified using the literature review. Using the collected data, multiple regression models were developed. The models showed that on the lightly vegetated roadways, people drove faster and drove much closer to the edges of the road. When the landscape changed to more vegetated, people drove much slower and drove closer to the centre of the road. Developed models also predict the speed selection of drivers and lateral positioning of the vehicles on the roadway sections. It was clear that the roadside vegetation influences the drivers’ speed selection and positioning of the vehicle on the road. Therefore, it is a necessity that the road designers would consider the effect of roadside vegetation on designing the roadway sections. Ultimately, it would reduce the number of runoff-the-road crashes happening in the country.