Speed Choice and Curve Radius on Rural Roads

In most developed countries the majority of serious injured and fatalities in traffic accidents can be associated with driving in rural areas. A significant part of these incidents can be connected to the alignment of the road and an inappropriate speed choice.
Often are curved alignments marked with informative speed-calming measures as traffic signs, reflectors or surface painting. However, it has been the hypothesis that people are reducing their speed insufficiently and are driving too fast in most curved alignments – especially when they are driving there frequently.
By knowing the speed near and in the curved alignments compared to the geometry of the curved alignments, it can be clarified, if and which speed-calming measures that are required. Using GNSS-based floating car data (FCD) from driving cars the speed near and in curved alignments is found. Single observation of FCD are connected to trips and these are summed in order to find the mean speed in the curved alignments. Data in the paper are partly based on FCD from the Intelligent Speed Adaptation (ISA) project, “Pay As You Speed” (PAYS) (http://www.sparpaafarten.dk/) and from the more present and big FCD project “ITS Platform” (http://www.itsplatform.dk/index.php/en.html). An initial result based on the data from PAYS only including 18 curved alignments with radiuses spanning from 15 to 350 m show that the coherence between speed and radiuses reveal a correlation that can be explained by the following logarithmic function where v is speed and R is radius.
V=14*ln(R)
The tentative results based alone on the “Pay As You Speed“ project show an expected positive connection between speed and radius, and that speed is virtually unchanged with a radius higher than 225m. In the final paper, a much bigger data sample from ITS Platform will be used to underpin the results presented here, but also to avoid any bias from PAYS data due to the speed reducing effect from the ISA.