Reliability of products and systems are fundamental to consumer choice. In the context of transport systems, journey time reliability is seen as a key determinant of traveller choices. Existing research has found that on-time arrival can be valued more than travel time savings. Thus, the quantification of reliability is paramount to monitoring and assessing the performance of transport systems, especially considering road transport systems. This paper presents the development of the Unified Reliability Model (URM), a supplementary tool for the simple and robust measurement of reliability on a road network. The URM unifies aspects of the UK Reliability Model and the New Zealand (NZ) model, both of which are currently applied as best practice. Applications of the URM using data from the Sydney road network present robust measurements of reliability that are comparable or exceed the accuracy of the existing approaches.