In this article, the authors address the problem of optimal guidance of road network users. In the literature, several routing algorithms have been proposed under different approaches to solve this problem. Most adaptive algorithms for optimal path are based on the least expected travel time. Another approach has emerged named the SOTA (stochastic on time arrival). This approach based on the idea of Frank (1969), which aims to maximize the probability of arriving to a destination node parting from a given node in the network and with a given time budget. The authors' contribution consists here in extending this approach in order to introduce robustness towards path failure, in the guidance optimization. The authors propose a model that includes the existence as well as the performance of detours for selected paths, in the calculus of the travel time reliability. This new way of calculating travel time reliability guarantees a kind of robustness of the optimal guidance strategy.