The use of risk criteria in comparing transportation alternatives

For the transportation of dangerous substances, several modes of transportation are possible. If there are
multiple possibilities, it is relevant to compare the safety of the transportation alternatives.
TNO has developed a consistent method to compare the different transportation modes, using standard
risk criteria like cumulated Individual Risk (Locational Risk) and Societal Risk.
An evaluation of the method was done for two typical cases: transport of 100,000 t/y ammonia and
100,000 t/y propane. By using a standard QRA (Quantitative Risk Assessment) tool, the individual risk
contours, the societal risk (FN) curve, and additional societal risk maps were generated and compared for
4 modes of transportation: railway, road, ship and pipeline
When using the Individual Risk contour as a criteria, the “distance to 10-6/y risk value” is often used to
compare risks of transport. Because of the important contribution of loading and unloading activities at the
beginning and endpoints of the route, one should evaluate the cumulated contours for interference with
vulnerable objects.
For Societal Risk, the Dutch prescribed approach would be to consider the FN-curve for the kilometre
segment of the route with the highest risk. The paper demonstrates that this approach may give
misleading results when comparing different route tracks. Furthermore, because stationary equipment is
subjected to stricter allowance rules (a lower guide value of societal risk curve), comparison of the
combined effect of the transport and stationary loading & unloading activities is ambiguous. By applying
societal risk maps, where (cumulated) risk is observed from the point of view of the receiver, this ambiguity
can be taken away. The usage of these maps can hence be considered a very valuable addition in ranking
risks of different alternatives