To improve the robustness and adaptation to node mobility, ad hoc routing protocol uses as route selection criterion, the route reliability metric between end points. In the first part of this paper, we derive an analytical closed form expression for the computation of route reliability metric, that takes into account dependencies between adjacent links. Based on our analytical formulation, the route reliability metric computation does not introduce any complexity. Simulations show that our model can obtain more accurate results than the traditional methods. However, the route reliability metric increases network resources used in terms of intermediate nodes between source and destination. It may also increase packet delay. Moreover, the interference and collision probability between packet increase when the number of relays in the same range increases. In order to overcome these inconveniences, in the second part of this paper, we propose a new routing metric which combines reliability and hop count criteria. Simulations results show that the introduced metric allows better results.