Hello, Thanks for the quick reactions again. Some reactions from my side on this:
1) Ok, I get it. So it is better to use a realistic average value. However, the default values are extremely high then, since realistic averages for acceleration and deceleration are below 2 m/s/s. 2) The documentation of vehicle definitions says "The drivers reaction time in seconds", so that is a bit misleading then. If I understand well, the distance to the leading vehicle depends on both the speed and tau, so the precise value of tau matters for this distance. However, reactions take x time steps, with x = ceil(tau / step-size)? So, 1 second time steps and a tau of 1 means a reaction takes 1 time step and for a tau of 1.1 a reaction would take 2 time steps? 3) Hmm, a speed factor of 0.2 is very low. It would make more sense to cap the distribution such that any drawn value cannot differ more from the mean than two standard deviations. So it is currently unlikely but possible that a vehicle receives a speed factor of 10 such that it always wants to drive at it's physical maximum speed? Best regards, Pieter On 22 April 2014 12:51, Jakob Erdmann <[email protected]> wrote: > Hello, > 1) Using the default car-following model, vehicles tend to drive as fast > as possible and then brake as hard as possible (using 'decel'). This means > they will brake with 'decel' at the latest possible moment when approaching > the jam. Thus 'decel' functions more like a desired deceleration. > Unfortunately, there is yet not concept for discriminating between desired > and maximum deceleration. > > 2) Tau is the desired time gap to the follower which may be interpreted as > a consequence of a drivers reaction time. However, reaction time is > fundamentally limited by simulation step size. This why you will get a > warning when using tau < step-size (it may lead to collisions). Also, when > setting tau > step-size, drivers will still adapt their behavior during > every simulation step. There are plans for adding a new car following model > which allows reaction times above the simulation step size to be modeled ( > http://sumo-sim.org/trac.wsgi/ticket/1151) > > 3) A normal distribution with expectation X may return any real value. > However, we wish to avoid very low speedFactors so we always return values > of at least 0.2. (The value in the wiki documentation was wrong and is now > fixed). > > regards, > Jakob > > > 2014-04-22 12:03 GMT+02:00 Pieter Loof <[email protected]>: > >> Hi all, >> >> Just a few short questions to make sure that I interpret the vehicle >> parameters correctly: >> >> 1. 'decel' is the maximum deceleration of vehicles, so the average value >> will be lower. Suppose a vehicle drives towards the end of a traffic jam, >> how large is the deceleration it will apply compared to this maximum >> value? >> 2. 'tau' is the reaction time. Suppose we have simulation steps of 1 >> second >> and a tau of 0.8, are vehicles then able to start reacting on a fraction >> in >> between two simulation steps? >> 3. 'speedDev' is the deviation for drawing a desired speed factor from a >> normal distribution. The documentation says "The resulting values are >> capped at 0.1 to prevent extreme dawdling." I don't understand this >> sentence, can someone explain this? >> >> Best regards, >> Pieter >> >> ------------------------------------------------------------------------------ >> Start Your Social Network Today - Download eXo Platform >> Build your Enterprise Intranet with eXo Platform Software >> Java Based Open Source Intranet - Social, Extensible, Cloud Ready >> Get Started Now And Turn Your Intranet Into A Collaboration Platform >> http://p.sf.net/sfu/ExoPlatform >> _______________________________________________ >> sumo-user mailing list >> [email protected] >> https://lists.sourceforge.net/lists/listinfo/sumo-user >> > > ------------------------------------------------------------------------------ Start Your Social Network Today - Download eXo Platform Build your Enterprise Intranet with eXo Platform Software Java Based Open Source Intranet - Social, Extensible, Cloud Ready Get Started Now And Turn Your Intranet Into A Collaboration Platform http://p.sf.net/sfu/ExoPlatform _______________________________________________ sumo-user mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/sumo-user
