Glossary of Data Variables for Fatal and accident causation ... - ERSO

Manual For SafetyNet accident causation system (SNACS)
6.5 Analysis with SNACS – principles and components
Before we go into the details of how to perform an accident analysis with
SNACS, it needs to be made very clear that the whole point of SNACS is to
make it possible to systematically describe and store what we know about the
reasons for an accident. SNACS in itself cannot tell us why the accident
happened. If it could, we would need neither the on-scene investigation nor the
interviews. What SNACS does is provide a structured way to sort out the
reasons we find for the accident, and classify them as belonging to a set of
categories developed from previous research. SNACS is an organiser of
explanations, not a provider.
Analysing an accident with SNACS takes place in two steps. First of all, an
evaluation of the context for the event is made. Secondly, a detailed analysis of
the accident is made, with the context description as support. The SNACS
method has two tools to do the analysis.
The first tool is a table called Common Performance Conditions (CPC), which is
used for context description and evaluation. Each CPC represents the state of a
contextual variable affecting the general performance of the driver and vehicle
in a traffic situation.
The second tool is a classification scheme that lists possible factors that can be
involved in making a driver and vehicle loose control of a situation. On the
highest level the scheme distinguishes between the effects that are present in a
situation, and the causes of or reasons for those effects. The effects are called
phenotypes (sometimes also referred to as critical events), and they refer to the
observable consequences of a dysfunctional behaviour. For traffic
accidentology, this is basically what you see when you arrive at the scene of an
accident. The causes or reasons for the effects are called genotypes. The
genotypes are used to describe what has brought about, or can bring about, the
effects.
The terms phenotype and genotype are deliberately chosen to reflect their
counterparts in biology. Two humans (two phenotypes) never look exactly the
same, but the underlying genotypes that generate their different looks are
identical for both. The same goes for accidents and near-misses; the looks are
different, but the set of possible underlying causes is the same. What differs
between looks is which subset of genes or causes that is dominant or active for
the particular situation (critical event/phenotype).
Causes typically cannot be observed, but must be inferred by reasoning. In
addition to listing possible causes/reasons for the phenotypes (critical events),
the SNACS classification scheme therefore also describe the links between
them. The links can be said to represent existing knowledge about how different
factors (causes and consequences) can interact with each other.
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