This paper will describe the Australian Road Research Board (ARRB) Travel Time Model for estimating arterial travel. Congestion in large urban centers has been increasing and the road networks of some capital cities often operate at near - or oversaturated conditions. In such conditions, it becomes critical for a road manager to have a clear picture of how the road network is performing in real-time. A road manager can benefit from network performance indicators such as travel times and their variability. A road user can also benefit from the same travel time information to avoid congestion by re-routing or varying trip start times. Travel times are now displayed on most freeways in Melbourne in real time. The estimation of arterial travel times is a more challenging task because arterials are interrupted facilities with signals and other control devices interrupting traffic flow times for general traffic and buses. The model retrieves traffic data from SCATS each minute and has been implemented in a server at VicRoads. This paper describes the calibration and validation processes and highlights challenges for estimating travel times without identifying individual vehicles.