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Newbie Help - Saturation Flow much too high with default car following model [message #1836404]

Sat, 02 January 2021 01:37

david stewart

Messages: 2
Registered: January 2021
Location: Brisbane Autralia

Junior Member

Hi Sumo Users

I hope it is appropriate for a newbie to ask for help in this forum.

I have created my first network using NetEdit Gui. I have a simple T junction with Traffic SIgnals. To test the saturation flow I have cut it down to just one route flow through the signals and configured the signals to have 45 seconds green and yellow and 45 seconds red (I will worry about lost time later). So, I would expect a flow rate of about one vehicle every 2 seconds that is a saturation flow of somewhere between 1800 and 2200 pcu per hour. That is 900 veh per hour through the signals with a 50% green time ratio. But I am getting a much higher flow rate of about 2,800 measured in the exit lane of the signals.
The simulation looks good in the GUI the vehicles are obeying the signals but when I single step through the simulation (presumably 0.1 seconds at a time I have not seen the simulation step documented anywhere yet) I see one vehicle crossing the stop ie ever 0.3 seconds

I understand that the saturation flow is a result of the car following model and I have looked at the default parameters for the Krauss model and all looks good.

I am using the default vehicle type which should use Krauss. I understand command line switches but would prefer to wirk with the GUI as far as possible.

What am I missing? Do I have to activate the Krauss model some where?

Thanks is advance for any suggestions. I will upload my files if none can suggest an obvious omission on my part. And of course, if anyone is prepared to help an old graybeard newbie.

Best Regards
David

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Re: Newbie Help - Saturation Flow much too high with default car following model [message #1836467 is a reply to message #1836404]

Tue, 05 January 2021 07:50

david stewart

Messages: 2
Registered: January 2021
Location: Brisbane Autralia

Junior Member

OK I have found two silly mistakes in my thinking. Single stepping through the simulation in the GUI apears to always be one second and flow is the number of vehcles over the detector per hour NOT during the 15 minute measurement period as I thought. nVehContrib is the number of veh over the period.

So my saturation flow rate is perhaps a bit low. I would expect 900 veh per hour with a green time ratio of 50%. So it is time to look at the intergreen time and start delay and end gain.

I have also added a line to my additionals file in the config time to set the simulation step time value = 01. I think it is working as the simulation took considerably longer to complete with the gui delay set to 0. But I am having a bit of a problem understanding how to use the config file with the GUI and keep overrighting my carefully handcrafted additional. But I will soldier on and hopefully solve my own problems before asking for more help.

Thanks to anyone who took the time to read my post. Sorry to have wasted your time.

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Re: Newbie Help - Saturation Flow much too high with default car following model [message #1841259 is a reply to message #1836467]

Sun, 09 May 2021 12:06

martin boyle

Messages: 3
Registered: May 2021

Junior Member

Before starting, it is important to know that a vehicle in SUMO consists of three parts: ... It is possible to define repeated vehicle emissions ("flow"s), which have the same ... In fact this is only relevant, when you define a lot of routes or have large gaps ... The default car following model is based on the work of Krauß but other

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Re: Newbie Help - Saturation Flow much too high with default car following model [message #1841313 is a reply to message #1841259]

Wed, 12 May 2021 03:06

martin boyle

Messages: 3
Registered: May 2021

Junior Member

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Re: Newbie Help - Saturation Flow much too high with default car following model [message #1841493 is a reply to message #1841313]

Wed, 19 May 2021 03:56

martin boyle

Messages: 3
Registered: May 2021

Junior Member

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