For the urban transport component of the Audit, the top-down economic analysis used for the other sectors, which is based on national accounts and industry data, was complemented by a bottom-up analysis based on detailed transport modelling for the six major capital cities.
This modelling provides detailed information about trips within these cities by origin/destination (O/D), and by corridor, in 2011. It takes account of projected population and employment growth and spatial distribution to project demand for trips, also by O/D and corridor, in 2031.
For both road and rail corridors the model includes detailed information about capacity, showing where demand is projected to grow in excess of supply. For road corridors it quantifies the cost of delay, showing where interventions will likely provide the biggest economic return. For rail corridors the model assumes minimal delay (i.e. all passengers are able to board the next available train). This is to ensure the model does not displace rail passengers, and thus shows the full extent of demand for the rail corridor.
Given the absence of rail delay cost from the model, projected delay cost for road corridors is at best an approximation. However, rail delay cost is unlikely to represent more than a small proportion of total delay cost for most corridors. As such, road delay cost is a reasonable proxy for delay cost for most corridors, and serves as a useful indicator of which corridors warrant further study.