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Re: [sumo-user] Question about reproducing the phenomenon "capacity drop"
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Hello Jakob,
Thanks very much for your reply. You are absolutely right.
Now I have set the merging area with four lanes but the downstream mainline with three lanes. Also, I have increased the input volume with the attributes departPos="random_free" and departSpeed="max". I didn't changed the default speed distribution but set the lane changing parameter lcCooperative to "0.6". By doing so, it seems "capacity drop" has happened. Am I on the right way?
Best,
Yu Tang
-----原始邮件-----
发件人:"Jakob Erdmann" <namdre.sumo@xxxxxxxxx>
发送时间:2019-04-02 21:28:39 (星期二)
收件人: "Sumo project User discussions" <sumo-user@xxxxxxxxxxx>
抄送:
主题: Re: [sumo-user] Question about reproducing the phenomenon "capacity drop"
Hello,
the answer to this is a bit complex, sorry.
- capacity drop is negatively correlated with lane count in reality. With default settings you should be able to see it if the main line has only 1 lane (2 lanes in the merging section)
- capacity drop can only be observed if the entering flow of the mainline is near the limit. In a small scenario this can be achieved with vehicle/flow attributes
departSpeed="max" departPos="last"
- however, using the default distribution of desired speeds (speed deviation of 10% around the speed limit) you will still not get the full capacity because sometimes a slow vehicle is inserted after a fast vehicle and this creates gaps in traffic. When these gaps are filled at the on-ramp this compensates for the capacity drop so you might actually see a capacity gain.The capacity drop can be observed when setting the speed deviation to a lower value (speeDev="0.05") and it grows stronger when setting it even lower
- there is a known issue with the current dynamics model that can lead to a strong separation of vehicle speeds between the lanes (rightmost lane is very slow and leftmost lane is still at maximum speed). This lowers the observed capacity drop effect because there is no spill-over jamming effect to the left lanes. The speed seperation can be avoided with careful tuning of the lane-changing gap acceptance parameter
(lcAssertive) distribution across the vehicle fleet but I anticipate that there will be model extensions in the future to adress this.
regards,
Jakob
Hello,
I am simulating the traffic in the merging area where vehicles come from the one-lane on-ramp and the three-lane mainline. I hope to reproduce the phenomenon "capacity drop" that means the discharge rate is less than the capacity in the downstream mainline. I have tuned some parameters but failed.
Can anyone kindly informed me which parameters should be fine-tuned to simulate "capacity drop"?
Thank you.
Yu Tang
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