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Re: [sumo-user] Gap acceptance in lane changing
The secureGaps are not only influenced by tau but also by vehicle speed. Changing tau can have a major influence on scenario dynamics including  average speeds so a naive interpretation of the distribution is misleading.

the *secureGap values in the lanechange-output are always those for lcAssertive 1 (because when the gaps are reduced due to lcAssertive this is not really secure anymore). What you would rather look at are the actual gap values (leaderGap, followerGap) which are influenced by lcAssertive.
As above, due to the influence of lcAssertive on scenario dynamics, the distribution of gaps is hard to interpret.
You could try to look at time-headways instead i.e. leaderGap/(leaderSpeed-speed)  or leaderGap/speed (also for the secureGaps).

regards,
Jakob


Am Di., 30. Juni 2020 um 14:52 Uhr schrieb Solmaz Razmi Rad - CITG <S.RazmiRad@xxxxxxxxxx>:

Hi Jakob,

 

Following our discussion below, I tried to run the simulation with different lcAssertive and tau values to see how they affect the value of requiredGap (in seconds) which is calculated as: “(secureBackGap + followerMinGap + subjectLength + subjectMinGap + secureFrontGap)/Speed” and derieved from the lane_change_output file.

 

To my surprise:

·       Tau did not influence the requiredGap at all. I tested tau=1.6 s (recommended for IDM) and tau=0.5 s. Both of them resulted in the same mean and standard deviation for requiredGap.

·       As you confirmed earlier, the requiredGap is divided by the value of lcAssertive. But the results did not support this one either. Running the simulation with lcAssertive=3 resulted in requiredGap ( μ= 6.0509, std=3.239) whereas lcAssertive=30 resulted in requiredGap ( μ= 6.107, std= 3.22). It seemed like the accepted gap is adjusted by some sort of a function of lcAssertive instead of a simple division and even Higher lcAssertive value resulted in higher requiredGap!

 

Am I doing some calculations wrong?

 

Regards,

Solmaz

 

 

From: sumo-user-bounces@xxxxxxxxxxx <sumo-user-bounces@xxxxxxxxxxx> On Behalf Of Jakob Erdmann
Sent: vrijdag 19 juni 2020 15:18
To: Sumo project User discussions <sumo-user@xxxxxxxxxxx>
Subject: Re: [sumo-user] Gap acceptance in lane changing

 

1) Yes

2) you can set minGap=0 to lower the size of accepted gaps. At high speeds you will not see adverse effects but gaps will probably appear too small at lower speeds. Some car-following models such as IDM require minGap as an additional buffer for collision-free driving.

 

Am Fr., 19. Juni 2020 um 11:55 Uhr schrieb Solmaz Razmi Rad - CITG <S.RazmiRad@xxxxxxxxxx>:

1.        So, the requireGap, depends on the followSpeed. And followSpeed should be also influenced by “tau”. Then the requireGap is always a function of tau. Is this right? Can I say, if I have a distribution for tau, I will have a variation for gap acceptance (requireGap)?

2.        And regarding the minGap, can I assume minGap=0 if lane change happens without any jam?

 

 

From: sumo-user-bounces@xxxxxxxxxxx <sumo-user-bounces@xxxxxxxxxxx> On Behalf Of Jakob Erdmann
Sent: vrijdag 19 juni 2020 11:39
To: Sumo project User discussions <sumo-user@xxxxxxxxxxx>
Subject: Re: [sumo-user] Gap acceptance in lane changing

 

1) yes

2) these are computed by the car-follow model functions. They generally are consistent with the followSpeed function so that neither the ego vehicle nor its follower on the target lane have to perform any extra braking after the lane change is completed.

3) if a jam develops immediately after lane changing, vehicles must still be able to maintain the configured minGap, thus the value is already considered during lane changing

 

 

 

Am Fr., 19. Juni 2020 um 11:26 Uhr schrieb Solmaz Razmi Rad - CITG <S.RazmiRad@xxxxxxxxxx>:

Hi there,

 

I am trying to investigate the impact of gap acceptance in lane changing around on-ramps on the capacity of a freeway. I want to use a distribution for the gaps accepted while lane changing. I realized that the parameter which controls the gap acceptance is “lcAssertive” (But if I understood correctly, lcAssertive can influence the size of accepted gap but it doesn’t define the gap itself) . The SUMO vehicle definitions state that "the required gap is divided by the value of lcAssertive". When searching for the definition of requiredGap, I came across this page ( http://sumo-user-mailing-list.90755.n8.nabble.com/sumo-user-lcAssertive-Behavior-td3244.html ) where Jakob explained about requiredGap:  “requiredGap = secureBackGap + followerMinGap + subjectLength + subjectMinGap + secureFrontGap”.

I have a couple of questions here:

1.        What exactly is requiredGap? Is this the same as the accepted gap in lane changing?

2.        How are secureBackGap or secureFrontGap defined? Is there any relation between tau and secureBackGap or secureFrontGap?

3.       From what I have understood, MinGap is the jam distance or the distance which vehicles keep when standstill. How does this contribute to gap acceptance in lane changing?

I appreciate your help in advance.

 

Regards,

Solmaz

 

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