1) I agree that 4.5m/s is probably to high for desired deceleration and more appropriate for a max deceleration. This is simply the historical baggage of the Krauss car-following model which does not distinguish between desired and max decel. Feel free to roll your own car following model (-: 2) The documetation at http://sumo-sim.org/wiki/Definition_of_Vehicles,_Vehicle_Types,_and_Routes#Car-Following_Modelshas been updated 3) Yes. extreme values are currently possible. It would be best to calibrate the cut-off using a real-world data set. Do you think it needs be made configurable?
regards, Jakob 2014-04-22 13:55 GMT+02:00 Pieter Loof <[email protected]>: > 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
