yes, I mean accel as in the vType parameter accel (defaulting to 2.6). I also find this a bit strange (but I didn't make this part of the model). setting sigma > 1 should simply increase the magnitude of speed fluctuations. While it is not tested, I don't think it will have a bad effect. Note, that sigma lets the vehicle drive slower in all situations (when accelerating and when braking) which may not be what you want. Setting accel to 6.5 on the other hand doesn't sound like a very good idea since vehicles generally do not accelerate that much. regards, Jakob
2014-02-24 16:17 GMT+01:00 v.f.baines <v.f.bai...@bath.ac.uk>: > Hi, > > OK just two bits to check then, when you say speed reduced by > accel*sigma*random - you definitely mean accel? Just seems strange, I > thought that value would just be used in increasing speed rather than > decreasing. > > And when you say high values, how high is high? In the docs it says sigma > is between 0 and 1? So it can be bigger than that you mean? And for accel, > high but feasible? Or just super high? Looks like default is 2.6, something > like 6.5 is feasible and 3 times bigger if thats high enough? > > Will experiment around with some numbers anyway, I just dont want to > accidentally break validity of models > > Thanks > > > -------- Original message -------- > From: Jakob Erdmann > Date:24/02/2014 13:13 (GMT+00:00) > To: vb...@bath.ac.uk > Cc: sumo-user > Subject: Re: [sumo-user] Creating congestion waves and measuring them > > Hello, > I have to retract an earlier statement due to a review of the computations > involving sigma. > > in the default car-following model (Krauss) there is no concept of >>>>>>> overbraking. Vehicles will always brake just hard enough to avoid a >>>>>>> crash. >>>>>>> >>>>>> > This was wrong. The speed of a vehicle is reduced by sigma * accel * > random in every simulation step regardless of whether the vehicle is > braking or accelerating (accel is the value of the vType attribute accel, > random is from [0,1]).This means that a braking vehicle will sometimes > drive slower than it needs to. > The fact that it scales with accel is up to debate but you should be able > to see a wave of increasing deceleration if you use high values of sigma > and accel. > > Vehicles should never crash as long as tau > step-size and unless you play > with speed mode or lane change mode. > If you really want a crash you can set the speed mode of a vehicle so as > to ignore maximum deceleration and then braker harder than it normally > could (and thus harder than the follower expected). > regards, > Jakob > > ------------------------------------------------------------------------------ Flow-based real-time traffic analytics software. Cisco certified tool. Monitor traffic, SLAs, QoS, Medianet, WAAS etc. with NetFlow Analyzer Customize your own dashboards, set traffic alerts and generate reports. Network behavioral analysis & security monitoring. All-in-one tool. http://pubads.g.doubleclick.net/gampad/clk?id=126839071&iu=/4140/ostg.clktrk _______________________________________________ sumo-user mailing list sumo-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/sumo-user
