Safety CaUsation, Benefits and Efficiency (SafetyCube) is a European Commission supported Horizon 2020 project with the objective of developing an innovative Road Safety Decision Support System (DSS). The DSS will enable policy-makers and stakeholders to select and implement the most appropriate strategies, measures, and cost-effective approaches to reduce casualties of all road user types and all severities. The three thematic pillars of SafetyCube, which have been tackled in parallel, are “Road Users”, “Infrastructure” and “Vehicles”.
This document represents the synthesized work conducted in order to identify road user related risk factors and countermeasures as well as to quantify their effect on road safety. Furthermore, it demonstrates the incorporation of developed contents into the Road Safety DSS (https://www.roadsafety-dss.eu/) and points out the specific challenges which make the research on road user related risks and measures distinct from the thematic areas “infrastructure” and “vehicles”.
Stakeholders and policy-makers have been involved in the project work early on. Their needs and perceived hot topics were considered to ensure the relevance of the DSS. The identification and assessment of road user related risk factors and countermeasures was conducted in a standardized manner following the methodology developed to be applied to all three thematic pillars (road user, infrastructure, vehicle).
Starting point was the creation of a taxonomy of topics (separate for risks and measures), followed by a systematic literature search and selection of studies for each of the identified topics (e.g. drink-driving, distraction, fatigue, diseases, speeding etc.). Only studies were selected which provide a quantitative estimate of effect on road safety – either in terms of accident occurrence or other safety performance indicators such as performance in a driving simulator or self-reported behaviour. The preferable assessment of accident outcomes is oftentimes, however, especially for risks and measures associated with humans, a challenging endeavour. Human risk factors are mainly not dichotomous variables which are either present or not but are rather on a spectrum and present to a certain extent which can vary over time (e.g. level of fatigue). Furthermore, they are often latent variables which are not observable and have to be inferred (e.g. by means of self-reports or psychometric tests). Eventually, they tend to not occur isolated from further risk factors and the level of entanglement can pose methodological challenges and the availability of e.g. crash modification factors is scarce. Also for road user countermeasures, the effect is not always extracted from a single measure but from combined intervention (e.g. campaigns).
Taking these considerations into account, studies were selected and the reported effects as well as further information like the research design were filled into a “coding template”. The predefined coding template was a valuable tool to collect information in a standardized way so that results are comparable. Effects per study are on the one hand fed into the database (which underlies the Road Safety DSS) together with the further study information. On the other hand, they are the basis for the risk factor/countermeasure analysis which then is summarized in a document, referred to as “synopsis”. These risk factor/countermeasure synopses are also available through the DSS. The overall effect assessment was conducted by either meta-analysis, vote-count-analysis or review type analysis. To provide a rough impression for the user at first glimpse, a four-staged “colour code” was assigned per topic (thus, per synopsis) to indicate the riskiness of a risk factor (note only three out of four colours could be assigned to the risk factors, no risk factor was qualified as green - no increased risk) or the effectiveness of a countermeasure. Furthermore, the synopses contain theoretical background on the risk factor/countermeasure and are prepared in different sections with distinct levels of detail for an academic as well as a non-academic audience. These sections are readable independently.
All the created synopses, underwent a self-imposed quality assurance procedure. At this point, due to this task, some of the synopses are still under review or being revised. As soon as the quality procedure is complete, further synopses will be introduced into the Road Safety DSS.
For 12 road user related countermeasures, an economic evaluation in terms of cost-benefit analysis and corresponding sensitivity analysis or an update of an existing cost-benefit analysis could be conducted. Within the SafetyCube project, European crash costs were updated (to 2015) and factors to correct for inflation as well as purchasing power parity were provided and applied to the measures costs. As outlined, effects in terms of accident reduction are not widespread for road user measures. Thus, the number of cost-benefit analysis is limited for this kind of road safety measures.