Date Published: February 4, 2019
Publisher: Public Library of Science
Author(s): Miguel A. Fernández, Luis Ángel García-Escudero, Aquilino Molinero, Costin Daniel Untaroiu.
Metal Road Safety Barriers (MRSB) are one of the devices implemented in roadsides to mitigate the consequences of run-off crashes. In Europe, they have to meet the requirements of the European Standard EN-1317-2. This article analyzes a set of run-off crashes against MRSB, for which an in-depth investigation has been performed, comparing them with the standard tests. It has been observed that in many of these real crashes, the barriers have not worked properly in spite of having passed these standard tests. This paper demonstrates which variables may be responsible for this, with the objective of helping to improve the current test standard through the analysis of new test variables.
Multidimensional Scaling, a dimension reduction multivariate statistical technique, has been used to better understand how real crashes compare to standard tests, using several impact variables at the same time. Then, a statistical analysis has been developed to show the influence of the “Relative orientation impact angle” on the performance of the MRSB.
Most of the real crashes analyzed are close to “TB11” and “TB32” standard tests. In many of these real crashes, the “Relative orientation impact angle” is very different from the “Impact angle”, and in these situations, the vehicle is not safely redirected to the road concerning the so-called “Exit-Box”.
MRSB are not working properly in some situations that are not far from the standard tests. To handle this, it could be interesting to include the “Relative orientation impact angle” as a control variable in new versions of the EN-1317-2 tests to guarantee the behavior of the MRSB. These results can help to adapt some test variables from the EN-1317-2 to what is happening in crashes.
Although around 1.25 million people die yearly on the roads, traffic crashes are predictable, preventable and, in particular, can be mitigated . In most countries around the world, about 30% of all road fatalities are single vehicle crashes , where one vehicle leaves the road and strikes a rigid object, rolls over or goes down a steep slope. Statistics illustrate the fact that when it comes to crash severity, run-off-road crashes are an important subset of crashes worldwide and crashes resulting from lane departure constitute a high proportion of severe or fatal crashes. For instance, the average fatality rate for this type of crashes accounted for approximately 1/3 of road deaths in the European Union [3, 4] or 53% of all fatal crashes in the United States . With the aim of mitigating the possible consequences of these single vehicle crashes, Road Restraint Systems (RRS) are installed in roadsides as they are one of the most efficient road infrastructure solutions. For example, the installation of a median barrier on a single carriage way in Israel resulted in a 23% estimated reduction of impacts and 50% estimated reduction in injuries , or the existence of RRS may reduce fatalities by a factor of four in France , of five in Belgium , or of three in some European studies  when compared to collisions against other road obstacles.
The use of statistical methods (MDS) allows us to better understand how close real crashes are to standard tests, using several impact variables at the same time. The collection of detailed information from real impacts can be useful, especially if these variables are treated together and compared with those coming from the tests. In this paper, it has been argued that most of the real crashes studied can be assigned to the impact tests necessary to obtain an “N2 containment level” for an RRS (meeting “TB11” and “TB32” tests). This suggests that these two types of tests are very interesting in run-off crashes, as they represent many usual real crashes.
While the conditions under which the standard tests are performed to assess the impact behavior of MRSB may be close to those of real crashes, we have seen that the set of variables considered for the tests seem not to be complete enough to properly describe the real situations, resulting in an unsafe impact behavior of the road safety barriers. The set of real crashes analyzed here suggests that it could be interesting to include the “Relative orientation impact angle” as a variable to be controlled in new versions of the EN-1317-2 standard, with the objective of helping to prevent injuries in run-off road crashes.