The model is intended as a post-processing module to be applied after a traffic model has been used to predict travel demand on a road network. Its output (the level of TTV) does not feed back into the traffic model to account for the behavioural response to TTV. The model is thus an example of a ‘Method 1’ approach in the terminology of de Jong and Bliemer (2015), who recommend using this simple type of model in the short run. Such approaches have been implemented in the Netherlands, the UK, the US and Sweden. In the longer run, they recommend working towards implementing the prediction of TTV and the behavioural response to TTV into the traffic models.

The prediction model is based on a statistical model of the relationship between observed travel times and traffic flows. Both travel time and traffic flow are dynamic processes that evolve over the day and affect each other. Our aim has been a simple model which takes into account the dynamic relationship between the two and avoids the potential endogeneity issues related to this relationship. In this respect, our model constitutes a significant methodological improvement compared to the traditional speed-flow curves.