## The weather impact on drivers speed choice

Student thesis: Master thesis (including HD thesis)

• Jeppe Hovaldt Jørgensen
4. term, Transport Engineering, Master (Master Programme)
Approximately 40 \% of traffic accidents in Denmark occur on rural roads. In 33 \% of these accidents speed is the main factor and has a significant influence on the severity of the accident. One of the many factors that have an influence on driving speed is weather conditions. Several international studies have examined different weather conditions and their influence on driving speed for various road types. In Denmark the Danish Road Directorate has made studies regarding how weather impacts speed on the motorway. However, there is limited knowledge surrounding weather conditions and their effect on rural roads in Denmark. This paper analyzes how temperature and wet pavement conditions influences driving speed on rural roads of Denmark.

Driving speed is analyzed using Floating Car Data from the research project ITS Platform and weather data from weather measurement stations of the type Vaisala. This paper builds on data from 15 different rural roads in Northern Jutland where 342 different cars have driven 27.000 trips over a 3-year period.
The data is categorized into 24 different groups, based on 6 temperature intervals of 5 $\decC$ and 4 different pavement conditions: dry, damp, wet and very wet. Using statistical tests and the average driving speed the following cases are examined: temperature impact, impact of the different pavement conditions and a combination of the two.

The results of this paper show that a decrease in temperature to under 0 $\decC$ gives a statistically significant reduction in speed, at approximately 3 km/h. This reduction is also reflected in the speed distribution, where a statistically significant variation is detected between frost and thaw. A further analysis of the temperature shows the variation between the categories doesn’t change significant ($\pm$ 1 km/h) when temperature is either above or below 0 $\decC$.

Analyzing dry and wet pavement conditions shows a statistically significant reduction in average speed by approximately 2 km/h. The further analysis of the pavement conditions shows a significant speed reduction when comparing the categories of dry and damp (2 km/h), wet and very wet (8 km/h). The distribution of speed as a result of the amount of water on the pavement shows a large dispersion in speed under very wet road conditions.
The result of analyzing the influence of both temperature and pavement conditions shows that both factors affect driving speed, especially in wet and cold weather conditions. Factors such as location and the characteristics of the individual driver also have a statistically significant influence on driving speed.

The study concludes that decreasing temperatures and wet pavement conditions reduces driving speed by an average of 2-3 km/h and even more then the two factors interact. It is also concluded that the drivers are more likely to reduce their speed due to the conditions of the pavement rather than the weather temperature they are driving in. However, it cannot be concluded whether the reduction in speed is sufficient in order to significantly increase driving safety under the examined weather conditions, which needs to be analyzed further.
Language Danish 7 Jun 2019 68
ID: 305326392