Re: [sumo-user] Use of minGap and Tau

[Jakob Erdmann <namdre.sumo@xxxxxxxxx>]

Assume that both vehicles drive at the same speed and with the same braking capability.

The leader vehicle starts to brake and the follower brakes 1s later.

In that second the follower covers the distance speed*1s and since both vehicles have the same braking distance, this leaves them standing at exactly minGap distance.

Note, that the relationship "Headway = minGap + speed*tau" only holds if both vehicles are driving with the same speed and have the same maximum deceleration. Otherwise it's more complicated.

Am Mi., 12. Aug. 2020 um 17:53 Uhr schrieb Bae, Jong In <jbae42@xxxxxxxxxx>:

Jakob,

Thank you for your reply. Just a follow up question: I now understand why minGap needs to be assigned with some values while driving. 

But at least with the Krauss model, it seems like the headway is currently determined by "Headway = minGap + speed*tau" while driving based on my observations.

If minGap is defined as 'minimum gap when standing' and is the value that needs to be achieved after the braking maneuver, could you please explain why minGap is affecting the headway while driving? Shouldn't it only act as more of a reference value during the deceleration process and the only headway parameter while standing?

Thank you!

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From: sumo-user-bounces@xxxxxxxxxxx <sumo-user-bounces@xxxxxxxxxxx> on behalf of Jakob Erdmann <namdre.sumo@xxxxxxxxx>
Sent: Wednesday, August 12, 2020 11:34 AM
To: Sumo project User discussions <sumo-user@xxxxxxxxxxx>
Subject: Re: [sumo-user] Use of minGap and Tau

 

I see your point. However, If the vehicles are required to maintain a given minimum gap while standing and also limit their deceleration to some fixed (desired) value then they need to consider that minGap already while driving so the minGap is achievable after the braking maneuver.

However, the above mostly pertains to the default Krauss model. Other models such as IDM are more lax in maintaining minGap and thus their headways will also be different.

Am Mi., 12. Aug. 2020 um 16:54 Uhr schrieb Bae, Jong In <jbae42@xxxxxxxxxx>:

Hello,

According to the SUMO documentation on vehicle definitions, both minGap (default = 2.2m) and Tau (default = 1s) are used to determine a vehicle's headway.

Is there a reason why both properties should be used while driving to characterize a realistic driving behavior? 

To my understanding, using both minGap and Tau would make the headway larger than the realistic value since they both contribute to determining the headway.

Should tau only be used while vehicles are moving whereas minGap should be only used while vehicles are standing?

If so, should they be muted (or be assigned with a value close to 0) for the vehicle status that is not applicable for them?

Thanks,

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