PTV Vissim 8 introduces mesoscopic simulation to the Vision Traffic Suite. This additional modelling level speeds up simulation by a factor of 50 compared to microscopic simulation. PTV Group is presenting the new feature for the first time at ITS World in Bordeaux (Booth A99).
“Users need to simulate increasingly large networks”, says Koenraad Verduyn, Director Solution Management at PTV Group. “With PTV Vissim 8 we have responded to this trend by introducing dynamic assignment even in medium-sized networks, as mesoscopic simulation is ideal for achieving quick computing times”. This allows users to observe the effects of phenomena such as blocking back or traffic light signals on journey times without having to wait for their computer systems to keep pace. This is made possible by the different level of detail involved.
A question of detail
In microscopic simulation, vehicle behaviour and interaction are modelled as close to reality as possible, whereas mesoscopic simulation is based on a greatly simplified model. “Individual vehicles are still simulated in mesoscopic simulation, but their behaviour is based on a car-following model which can be solved very efficiently with an event-based approach”, says Dr. Arne Schneck, software developer and expert in mesoscopic simulation at PTV Group. Unlike microscopic simulation, vehicle data is not updated at every time interval, but only at specific times. This might be when a vehicle enters a network link or reaches the end of a link. Another advantage is the fact that mesoscopic simulation provides a convenient way to calibrate networks due to the limited number of parameters. The simulation is more stable with respect to minor network changes which also means that phenomena such as gridlocks, where vehicles block each other’s way, occur less frequently.
How is mesoscopic simulation integrated with microscopic simulation in PTV Vissim and with macroscopic simulation in PTV Visum? “Networks already created in PTV Visum can be very easily transferred to PTV Vissim, where they can be simulated mesoscopically”, explains Schneck. “If users need to go into detail on specific routes or junctions, they can do this through a hybrid simulation”. This involves users specifying sections of the mesoscopic simulation in which all modes of transport and their interactions – including pedestrians and cyclists – will be simulated at a microscopic level. “This combines the high speed of mesoscopic simulation with the level of detail provided by microscopic simulation”, says Schneck.
This post is also available in: German