City of Zaragoza
Determine the short and long-term impact of a new tramway on Zaragoza’s road network.
This project showcases the merits of an iterative micro/macro approach over the typical “top-down” approach of deriving the origin-destination matrices with macro and inputting this data into micro. ￼
Our task was to determine the Origin-Destination matrix for the study area by means of a “traversal”, where the trips that enter, exit or stay within the sub-area are captured and a sub-matrix is generated. But the Zaragoza case shows that what happens next during scenario analysis will often invalidate that initial matrix.
In the first step of the study, we used the macro model of the entire city to determine the global OD matrix for both public transport and private cars. Once calibrated and validated against field measurements, we used the macroscopic model to compute a traversal matrix for the study area.
Finally, we calibrated the micro-simulation model inside the study area using the traversal demand as input and additional field measurements.
With the base model calibrated, we were ready to consider the future scenario that included the new tramway and a full priority tram pre-emption system at intersections.
Tram pre-emption is a typical situation where microsimulation outshines other models as it allows a second-by-second monitoring of a vehicle’s position.
The outputs of the simulation showed significant congestion at tramway intersections. Taken at face value, this would suggest that the new tramway would generate a critical decrease in performance for private vehicle flows and the possible rejection of the proposal.
However, in reality the process of transition would not be abrupt and drivers would gradually adopt new routes. In other words, the structure of the sub-matrix would change.
Applying the macro-micro iterative process, the Aimsun team fed the new street capacities derived from the micro simulation of the future scenario to the macro model and then used it to re-compute the traversal matrix.
The results of this second simulation show that, following a period of adaptation, traffic would be redistributed and congestion levels would return to acceptable levels i.e., that the new tramway would be viable. Indeed, the first phase of Zaragoza tram Line 1 entered service in April 2011, following successful completion of trials.