The use of simulation for traffic engineering assessments at the planning level is now extremely well established. Simulation outputs lie at the heart of decisions relating to public transport priority, intersection design, toll plaza, and congestion relief schemes. However, until recently, the use of simulation for operational decision support was thought to be out of bounds. So why was that and what has changed since?
‘Non-believers’ claim that CPU and data requirements for real-time applications are prohibitive. But are they? As part of its i-transport platform, the Land Transport Authority has built an Aimsun microsimulation model of the entire city of Singapore. The city of Madrid’s Aimsun Online model includes 50% of Madrid city center. On a powerful computer, these models run between 10 and 20 times faster than real-time. As for their insatiable data requirements, the Madrid model is calibrated against data from 480 detectors and the Singapore model includes a full interface with SCATS, emulating adaptive traffic control to perfection. With mesoscopic and hybrid mesosimulation-microsimulation added to the mix, the possibilities increase and the technical challenges of the past become (important) implementation details.
But is there a need for all this? The answer is a resounding ‘yes’. Granted, human competence and experience accumulated over the years enables today’s traffic managers to handle repeatable local peaks, such as a queue on a particular motorway exit during the morning rush-hour. But the trouble comes with non-recurring events, such as incidents: these never quite happen the same way or in the same place. Trying to alleviate congestion by reacting locally very often causes unexpected domino effects that are even harder to manage, and this can easily spiral out of control, leading to hours of delays and frustration for everyone involved.
Real-time simulation is possible and can provide a valuable weapon in the form of foresight. By allowing operators to fill information gaps in space (across the network) and in time (fast-forwarding to the future), simulation-based decision support frees up traffic managers to focus on what they do best – devising response strategies that the system evaluates against their often complex and conflicting objectives.
So is simulation-based decision support for traffic operations the future? What can be said for sure is that this used to be a technical question. It is now fast turning into a simple question of willingness to embrace innovation and to do the right thing.
Written by Dr Alexandre Torday and Alex Gerodimos, TSS-Transport Simulation Solutions, Spain. For more information, please log on to www.aimsun.com
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