In the attached file there are 2 images. On the left is the relative speed vs front to rear distance from following reference:
Wiedemann, R., Reiter, U., 1992. Microscopic traffic simulation: the simulation system MISSION, background and actual state. Proj. ICARUS Final Report. Brussels, CEC 2.
On the right is almost the same figure from VISSIM 5.40 manual. The perception threshold SDV on the left figure represents the point where driver realizes a slow vehicle ahead and then takes some time to react. On the right figure this happens instantaneously. Which figure is correct and what does the SDV actually represents, perception or reaction after perception?
The thresholds of perception in this model are the different actions taken by the driver during vehicle tracking. That is, the process of acceleration, deceleration, speed changes, rapprochement between vehicles, etc. The thresholds represent the invisible boundaries in each change made by the driver.
The model is a combination of driver behavior on the vehicle and the different actions that can be performed on the vehicle, so the unit used in the development of this model is vehicle-driver.
Thanks @Alma Valladares. But my question is directed specifically to threshold SDV. I am already familiar with the concept of thresholds and actions in Wiedemann's model.
Oh!, sorry, there was misunderstood your concern.
In the annexes attached thesis is a Spanish translation of the original article Wiedemann with detailed explanation of the thresholds.
@ Alma Valladares, unfortunaley I don't understand Spanish. Do you have any English translation?
Hi Umair,
inthe general context of Wiedemann's model, there is a perception threshold (the point when a driver is able to perceive that he is approaching a vehicle) and after some reaction time, the actual reaction takes place. To illustrate this, the left diagram is "correct". In the VISSIM implementation of W74, there is no reaction time explicity modelled. Instead, the thresholds are used as "action thresholds", i.e. when a driver comes across a threshold, he will react in the next timestep. If you consider this, the right diagram is also "correct", at least for VISSIM.
Hi,Umair Durrani .Would you please send me the paper"Wiedemann, R., Reiter, U., 1992. Microscopic traffic simulation: the simulation system MISSION, background and actual state. Proj. ICARUS Final Report. Brussels, CEC 2"?My email adress is [email protected] you very much.
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