  We introduce a unifying model to study the impact of worst-case latency
deviations in non-atomic selfish routing games. In our model, latencies are
subject to (bounded) deviations which are taken into account by the players.
The quality deterioration caused by such deviations is assessed by the
$\textit{Deviation Ratio}$, i.e., the worst-case ratio of the cost of a Nash
flow with respect to deviated latencies and the cost of a Nash flow with
respect to the unaltered latencies. This notion is inspired by the
$\textit{Price of Risk Aversion}$ recently studied by Nikolova and Stier-Moses.
Here we generalize their model and results. In particular, we derive tight
bounds on the Deviation Ratio for multi-commodity instances with a common
source and arbitrary non-negative and non-decreasing latency functions. These
bounds exhibit a linear dependency on the size of the network (besides other
parameters). In contrast, we show that for general multi-commodity networks an
exponential dependency is inevitable. We also improve recent smoothness results
to bound the Price of Risk Aversion.
