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eclipse-sumo / sumo

Eclipse SUMO is an open source, highly portable, microscopic and continuous traffic simulation package designed to handle large networks. It allows for intermodal simulation including pedestrians and comes with a large set of tools for scenario creation.
https://eclipse.dev/sumo
Eclipse Public License 2.0
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About IDM model #14073

Open adoreador opened 7 months ago

adoreador commented 7 months ago

I have a question about IDM model: In my simulation scenario, I have set up a single-lane road with two vehicles. The simulation time step is 0.1 seconds. For the following vehicle, I've chosen the IDM model with the parameters: minGap="2.5", accel="3", decel="3.4", tau="0.9", stepping="0.1" length="5", desiredMaxSpeed="33.34". When the two vehicles reach a stable state, their speeds are 29.466, and the speed difference is negligible. However, when I retrieve the longitudinal gap using traci.vehicle.getposition, I get a gap of 51.477 - 5 = 46.477. Why isn't the gap equal to minGap + v tau = 2.5 + 0.9 29.466?

In other words, why is the actual “time gap on the lane” not equal to the “desired headway” value in the stable state? Why don't vehicles proactively accelerate to reduce the following distance and achieve the desired spacing between two cars?

m-kro commented 7 months ago

This question can be answered best with an example scenario, as one needs to reach a stable state and you mention a specific IDM parametrisation.

adoreador commented 7 months ago

I apologize for any confusion caused by my earlier expression, and I sincerely apologize for that. I have rephrased my question. The situation I am facing pertains to a problem encountered while using IDM with a car following model during the simulation process. I am seeking your guidance on this matter, and I haven't resolved the issue yet. Once again, I apologize for any confusion caused by my previous miscommunication.

m-kro commented 7 months ago

Can you please check if the problem persists if you choose a speed below the edge speed limit for the leader vehicle? (see #14077)

adoreador commented 7 months ago

Thank you for your response!

Indeed, as mentioned earlier, the speeds of 29.46 in my designed scenario are all below the speed limit on my road. However, no matter how I adjust “accel” and “decel”, once they reach a stable state, the following vehicle maintains a constant gap instead of actively accelerating to achieve the desired gap of minGap + V * tau.

m-kro commented 6 months ago

I had a look into the original IDM model definition (as given on Wikipedia). In a following situation, the "interaction term" regarding the gap will not exactly reach minGap + v*tau. Even very small speed differences can make the gap grow over time such that it becomes way off minGap + v*tau from the formula. If you have access to the "Traffic Flow Dynamics" book, there is a chapter about how IDM fits platooning purposes (or not).

adoreador commented 6 months ago

Thanks for the answer!