Online meets Offline

Road in Paris

Online simulation is the ideal solution for improving traffic flow and road network utilisation.

Online simulation is the ideal solution for improving traffic flow and road network utilisation. PTV Optima developed by SISTeMA and PTV Group is a tool which provides dynamic traffic projections that are ahead of “real” time.

Traffic managers know from experience what traffic is going to be like during a specific time and day of the week and can therefore handle incidents which occur regularly. They use real-time information from detector data, floating car data (FCD) and cameras. However, these data records only cover a certain part of the area. A daily challenge – because if something unusual happens or if several unprecedented incidents occur at once, traffic managers will get stressed quickly. So they need support. Cities and regions, such as the Piedmont Region (Italy), London and Hong Kong, are therefore increasingly making use of online simulation as a decision-making tool. Their overall aim is to improve the traffic situation. Using PTV Optima is one way to achieve this goal. This model-based solution combines the tried-and-tested offline transport modelling method with real-time data and algorithms.

Infographic showing the interplay of PTV Visum, PTV Optima and the the traffic management system

PTV Visum processes travel demand data offline and provides PTV Optima with a basic simulation of the network. PTV Optima then uses real-time data from the traffic management system and provides up-to-date traffic information and traffic forecasts. Moreover, it assists traffic managers in evaluating their strategy.

“This process is based on a transport model created in PTV Visum which shows each “typical day” (e.g. working days or weekends) for the selected transport area,” explains Thomas Otterstätter, Product Manager for PTV Optima. “It models transport services and travel demand using demand matrices.” Based on this data and dynamic traffic assignment PTV Visum calculates the time-related traffic volume and turning movements in networks. All information is then transferred to PTV Optima. This is where online data comes into play. In PTV Optima, the data is used in real time in order to adjust capacity, speed and volume from PTV Visum’s base model to the current local flow and road conditions.

A glimpse into the near future

“As PTV Optima explicitly includes the network structure, traffic flow dynamics and the route choice behaviour of road users, it also covers the traffic situation for routes where no detectors are installed,” says Otterstätter. Moreover, the model-based solution can predict the impacts of unforeseen incidents and assess and compare various strategic actions. PTV Optima provides traffic forecasts which simulate a customizable time horizon of up to 60 minutes The user can immediately see the impact of traffic volume, speed and jams on the relevant road sections.

Screenshots of PTV Optima showing forecasts up to 45 minutes

PTV Optima enables traffic managers to predict the development of traffic in the near future (up to 60 minutes). This example shows a congestion evolution due to an accident. Red-coloured bars indicate critical areas.

Scenario-based strategic thinking

If there are too many incidents on the road network, it is important to quickly identify the problems and respond accordingly. Typical tools which allow planners to respond to this are traffic signal systems, dynamic lane operation, dynamic signs and traffic information via radio stations or the Internet. Today, they are used in real life in order to relieve traffic jams. The strategy chosen for the specific situation may have the desired effect. But that way, planners will never find out whether another strategy would have been even more efficient. If that is the case, wouldn’t it be better to test the various strategies in a virtual environment?

Strategies created offline in PTV Visum, for example, could be transferred to PTV Optima’s online environment where they are analysed, compared and listed before being rolled out. PTV Optima can compute a combination of several scenarios simultaneously within a few minutes so that the best strategy can be implemented as quickyl as possible. This procedure will expand the traffic manager’s scope of experience regarding unforeseen incidents. He will become more familiar with the different scenarios and can select the optimum strategy from the selection of measures recommended by PTV Optima, allowing him to remedy the situation as quickly as possible.