In the context of the development of the road safety audit procedure it showed up that together with the evaluation of the determined safety deficits/gains the quantification of the effects of these deficits/gains is appropriately on the road safety.
Thus a quantitative evaluation can take place, which indicates direct changes for the accident frequency and accident weight. It is also basis for a monetary evaluation.
The aim of this research was, based on known research reports, to search, to analyse and to develop tools for the quantification of the effects of safety-relevant differences and changes in context of a road safety audit.
Provision of the project results is made by a systematic evaluation of studies, expert reports, appraisals and literature documentation regarding quantified relationships between variables of the system and the traffic flow as well as other influencing factors and variables such as accident frequency, severity and types of accidents. A large selection of such documents is known. The desired relationships can respectively be filtered out by appropriate evaluations, analyses and calculations of the mentioned documents.
The first step was to make lists of safety-relevant parameters of infrastructure and of traffic operation based on standards and guidelines. The lists were completed with the safety requirements for each parameter (standard value, guideline value, recommendation) and so these lists can be used as checklists for a safety audit.
The second step was to search and to analyse correlations between the defined safety relevant parameters and accident parameters. Based on this, a first collection of quantification tools for Switzerland was developed. This is a temporary list of such tools which has to be specified and completed in the future.
Based on standards and guidelines, more than 300 safety-relevant parameters of road infrastructure and traffic operation were compiled and structured in 22 checklists. With these checklists a quantitative and qualitative evaluation and an assessment of the differences between the elected and standard or recommended values or between the elected values in the project and the values in the present situation is possible.
There are in principle two different types of tools for quantification. On the one hand, correlations between accident risk and parameters of infrastructure and traffic operation could be identified. With these correlations it is possible to estimate the effects on the road safety, which means the accident frequency and severity in the future. On the other hand, there are percentage-values about the influence of changing a parameter of infrastructure and traffic operation.
The stated values of the changes of accidents parameters are average values which have to be adjusted with a corresponding evaluation (experience) in every specific situation.