SigmaRL: A Sample-Efficient and Generalizable Multi-Agent Reinforcement Learning Framework for Motion Planning

• SigmaRL: A Sample-Efficient and Generalizable Multi-Agent Reinforcement Learning Framework for Motion Planning
  • Welcome to SigmaRL!
  • Install
  • How to Use
    • Training
    • Testing
  • Customize Your Own Maps
  • Papers
    • 1. SigmaRL
    • 2. XP-MARL
    • 3. MTV-Based CBF
    • 4. Truncated Taylor CBF (TTCBF)
    • 5. CBF-Based Safety Filter
    • 6. CPM Lab Benchmark
  • TODOs
  • Acknowledgments

Note

• Check out our recent work CBF-Based Safety Filter! It proposes a real-time CBF-based safety filter for safety verification of learning-based motion planning with road boundary constraints (see also Fig. 5).
• Check out our recent work Truncated Taylor CBF! It proposes a new notion of high-order CBFs termed Truncated Taylor CBF (TTCBF). TTCBF can handle constraints with arbitrary relative degrees while using only one design parameter to facilitate control design (see also Fig. 4).

Welcome to SigmaRL!

This repository provides the full code of SigmaRL, a Sample efficiency and generalization multi-agent Reinforcement Learning (MARL) for motion planning of Connected and Automated Vehicles (CAVs).

SigmaRL is a decentralized MARL framework designed for motion planning of CAVs. We use VMAS, a vectorized differentiable simulator designed for efficient MARL benchmarking, as our simulator and customize our own RL environment. The first scenario in Fig. 1 mirrors the real-world conditions of our Cyber-Physical Mobility Lab (CPM Lab). We also support maps handcrafted in JOSM, an open-source editor for OpenStreetMap. Below you will find detailed guidance to create your OWN maps.

(a) CPM scenario.	(b) Intersection scenario.
(c) On-ramp scenario.	(d) "Roundabout" scenario.

Figure 1: Demonstrating the generalization of SigmaRL (speed x2). Only the intersection part of the CPM scenario (the middle part in Fig. 1(a)) is used for training. All other scenarios are completely unseen. See our SigmaRL paper for more details.

Figure 2: We use an auxiliary MARL to learn dynamic priority assignments to address non-stationarity. Higher-priority agents communicate their actions (depicted by the colored lines) to lower-priority agents to stabilize the environment. See our XP-MARL paper for more details.

(a) Overtaking scenario with Center-to-Center (C2C)-based safety margin (traditional).	(b) Overtaking scenario with Minimum Translation Vector (MTV)-based safety margin (ours).
(c) Bypassing scenario with C2C-based safety margin (traditional).	(d) Bypassing scenario with MTV-based safety margin (ours).

Figure 3: Demonstrating the safety and reduced conservatism of our MTV-based safety margin. In the overtaking scenario, while the traditional approach fails to overtake due to excessive conservatism (see (a)), ours succeeds (see (b)). Note that in the overtaking scenario, the slow-moving vehicle $j$ purposely obstructs vehicle $i$ three times to prevent it from overtaking. In the bypassing scenario, while the traditional approach requires a large lateral space due to excessive conservatism (see (c)), ours requires a smaller one (see (d)). See our MTV-Based CBF paper for more details.

(a) The standard HOCBF approach requires tuning two parameters (lambda_1 and lambda_2).

(b) Our TTCBF HOCBF approach requires tuning only one parameter (lambda_1).

Figure 4: Our TTCBF approach reduces the number of parameters to tune when handling constraints with high relative degrees. See our TTCBF paper for more details.

(a) An undertrained RL policy without our safety filter often caused collisions with road boundaries.

(b) Our safety filter successfully avoided all collisions caused by the undertrained RL policy.

Figure 5: Demonstration of our safety filter for safety verification of an undertrained RL policy. See our CBF-Based Safety Filter Paper for more details.

Install

SigmaRL supports Python versions from 3.9 to 3.12 and is also OS independent (Windows/macOS/Linux). It's recommended to use a virtual environment. For example, if you are using conda:

conda create -n sigmarl python=3.12
conda activate sigmarl

We recommend installing sigmarl from source:

• Clone the repository

  git clone https://github.com/bassamlab/SigmaRL.git
  cd SigmaRL
  pip install -e .

• (Optional) Verifying the Installation by first launching your Python interpreter in terminal:

  python

  Then run the following lines, which should show the version of the installed sigmarl:

  import sigmarl
  print(sigmarl.__version__)

How to Use

Training

Run main_training.py. During training, all the intermediate models that have higher performance than the saved one will be automatically saved. You are also allowed to retrain or refine a trained model by setting the parameter is_continue_train in the file sigmarl/config.json to true. The saved model will be loaded for a new training process.

sigmarl/scenarios/road_traffic.py defines the RL environment, such as the observation function and reward function. Besides, it provides an interactive interface, which also visualizes the environment. To open the interface, simply run this file. You can use arrow keys to control agents and use the tab key to switch between agents. Adjust the parameter scenario_type to choose a scenario. All available scenarios are listed in the variable SCENARIOS in sigmarl/constants.py. Before training, it is recommended to use the interactive interface to check if the environment is as expected.

Testing

After training, run main_testing.py to test your model. You may need to adjust the parameter path therein to tell which folder the target model was saved. Note: If the path to a saved model changes, you need to update the value of where_to_save in the corresponding JSON file as well.

Customize Your Own Maps

We support maps customized in JOSM, an open-source editor for ​OpenStreetMap. Follow these steps (video tutorial available here):

• Install JOSM from the website given above.
• To get an empty map that can be customized, do the following:
  • Open JOSM and click the green download button
  • Zoom in and choose an arbitrary place on the map by drawing a rectangle. The area should be as empty as possible.
  • Clicking "Download" will open a new window. There should be the notification that no data could get found, otherwise redo choosing the area.
• Customize the map by drawing lines. Note that all lanes you draw are considered center lines. You do not need to draw left and right boundaries, since they will be determined automatically later by our script with a given width. The distance between the nodes of a lane should be approximatly 0.1 meters. You can find useful hints and commands for customizing the map at Actions and Tools.
• Give each lane the key "lanes" and an unique value.
• Save the resulting .osm file and store it at assets/maps. Give it a name.
• Go to utilities/constants.py and create a new entry in the dictionary "SCENARIOS" for it. The key of the entry is the name of the map and the value is a dictionary, for which you should at least give the value for the key map_path, lane_width, and scale. Also you should provide a list for reference_paths_ids (which paths exist?) and a dictionary for neighboring_lanelet_ids (which lanes are adjacent?).
• Go to utilities/parse_osm.py. Adjust the parameters scenario_type and run it.

Figure 6: Overview of currently available maps.

Papers

If you use this repository, please consider to cite our papers.

1. SigmaRL

Jianye Xu, Pan Hu, and Bassam Alrifaee, "SigmaRL: A Sample-Efficient and Generalizable Multi-Agent Reinforcement Learning Framework for Motion Planning," 2024 IEEE 27th International Conference on Intelligent Transportation Systems (ITSC), 2024.

• BibTeX

  @inproceedings{xu2024sigmarl,
    title = {SigmaRL: A Sample-Efficient and Generalizable Multi-Agent Reinforcement Learning Framework for Motion Planning},
    booktitle = {2024 IEEE 27th International Conference on Intelligent Transportation Systems (ITSC)},
    author = {Xu, Jianye and Hu, Pan and Alrifaee, Bassam},
    year = {2024},
    pages = {768--775},
    doi = {10.1109/ITSC58415.2024.10919918}
  }

• Reproduce Experimental Results in the Paper:

  • Git checkout to the corresponding tag using git checkout 1.2.0
  • Go to this page and download the zip file itsc24.zip. Unzip it, copy and paste the whole folder to the checkpoints folder at the root of this repository. The structure should be like this: root/checkpoints/itsc24/.
  • Run sigmarl/evaluation_itsc24.py.

  You can also run testing_mappo_cavs.py to intuitively evaluate the trained models. Adjust the parameter path therein to specify which folder the target model was saved. Note: The evaluation results you get may deviate from the paper since we have meticulously adjusted the performance metrics.

2. XP-MARL

Jianye Xu, Omar Sobhy, and Bassam Alrifaee, "XP-MARL: Auxiliary Prioritization in Multi-Agent Reinforcement Learning to Address Non-Stationarity," arXiv preprint arXiv:2409.11852, 2024.

• BibTeX

  @article{xu2024xp,
    title={{{XP-MARL}}: Auxiliary Prioritization in Multi-Agent Reinforcement Learning to Address Non-Stationarity},
    author={Xu, Jianye and Sobhy, Omar and Alrifaee, Bassam},
    journal={arXiv preprint arXiv:2409.11852},
    year={2024},
  }

• Reproduce Experimental Results in the Paper:

  • Git checkout to the corresponding tag using git checkout 1.2.0
  • Go to this page and download the zip file icra25.zip. Unzip it, copy and paste the whole folder to the checkpoints folder at the root of this repository. The structure should be like this: root/checkpoints/icra25/.
  • Run sigmarl/evaluation_icra25.py.

  You can also run testing_mappo_cavs.py to intuitively evaluate the trained models. Adjust the parameter path therein to specify which folder the target model was saved.

3. MTV-Based CBF

Xu, Jianye, and Bassam Alrifaee. “A Learning-Based Control Barrier Function for Car-Like Robots: Toward Less Conservative Collision Avoidance.” European Control Conference (ECC), 2025.

• BibTeX

  @inproceedings{xu2025learningbased,
    title = {A Learning-Based Control Barrier Function for Car-Like Robots: Toward Less Conservative Collision Avoidance},
    booktitle = {2025 European Control Conference (ECC)},
    author = {Xu, Jianye and Alrifaee, Bassam},
    year = 2025,
    pages = {988--995},
    doi = {10.23919/ECC65951.2025.11187043}
  }

• Reproduce Experimental Results in the Paper:

  • Go to this page and download the zip file ecc25.zip. Unzip it, copy and paste the whole folder to the checkpoints folder at the root of this repository. The structure should be like this: root/checkpoints/ecc25/.
  • Run sigmarl/evaluation_ecc25.py.

4. Truncated Taylor CBF (TTCBF)

Jianye Xu and Bassam Alrifaee, "High-Order Control Barrier Functions: Insights and a Truncated Taylor-Based Formulation," arXiv preprint arXiv:2503.15014, 2025.

• BibTeX

  @article{xu2025highorder,
    title = {High-Order Control Barrier Functions: Insights and a Truncated Taylor-Based Formulation},
    author = {Xu, Jianye and Alrifaee, Bassam},
    journal = {arXiv preprint arXiv:2503.15014},
    year = {2025},
  }

• Reproduce Experimental Results in the Paper:

  • Git checkout to the corresponding tag using git checkout 1.3.0
  • Run sigmarl/hocbf_taylor.py.

5. CBF-Based Safety Filter

Jianye Xu, Chang Che, and Bassam Alrifaee, "A Real-Time Control Barrier Function-Based Safety Filter for Motion Planning with Arbitrary Road Boundary Constraints," IEEE 28th International Conference on Intelligent Transportation Systems (ITSC), in Press, 2025.

• BibTeX

  @inproceedings{xu2025realtime,
    title = {A Real-Time Control Barrier Function-Based Safety Filter for Motion Planning with Arbitrary Road Boundary Constraints},
    booktitle = {2025 IEEE 28th International Conference on Intelligent Transportation Systems (ITSC), in Press},
    author = {Xu, Jianye and Che, Chang and Alrifaee, Bassam},
    year = 2025
  }

• Reproduce Experimental Results in the Paper:

  • Git checkout to the corresponding tag using git checkout 1.4.0
  • Go to this page and download the zip file itsc25.zip. Unzip it, copy and paste the whole folder to the checkpoints folder at the root of this repository. The structure should be like this: root/checkpoints/itsc25/.
  • Run sigmarl/evaluation_itsc25.py.

6. CPM Lab Benchmark

Julius Beerwerth, Jianye Xu, Simon Schäfer, Fynn Belderink, and Bassam Alrifaee, "From Simulation to Reality: A Benchmark for MARL in the Cyber-Physical Mobility Lab," arXiv preprint arXiv:TBD, 2025.

• Reproduce Experimental Results of the SigmaRL Simulation in the Paper:

  • Git checkout to the corresponding tag using git checkout 1.5.0
  • Go to this page and download the zip file at25.zip. Unzip it, copy and paste the whole folder to the checkpoints folder at the root of this repository. The structure should be like this: root/checkpoints/at25/.
  • Run sigmarl/eva_at25/run_models_parallel.py to evaluate the downloaded models. The evaluation results will be saved automatically.
    • This script requires Python parallel workers.
    • Alternatively, you can run sigmarl/eva_at25/run_models.py if you do not want to use parallel workers.
  • After the evaluation, run sigmarl/eva_at25/marl_aggregated_evaluation.py to analyze the evaluation results and obtain the performance metrics.

TODOs

• Improve safety
  • Integrating Control Barrier Functions (CBFs)
    • Proof of concept with two agents (see the MTV-Based CBF paper here)
    • High-Order CBFs (see the TTCBF paper here)
    • Collision aovidance with road boundaries (see the CBF-Based Safety Filter paper here)
  • Integrating Model Predictive Control (MPC)
• Address non-stationarity
  • Integrating prioritization (see the XP-MARL paper here)
• Effective observation design
  • Image-based representation of observations
  • Historic observations
  • Attention mechanism
• Misc
  • OpenStreetMap support (see guidance here)
  • Contribute our CPM scenario as an MARL benchmark scenario in VMAS (see news here)
  • Update to the latest versions of Torch, TorchRL, and VMAS
  • Support Python 3.11+

Acknowledgments

This research was supported by the Bundesministerium für Digitales und Verkehr (German Federal Ministry for Digital and Transport) within the project "Harmonizing Mobility" (grant number 19FS2035A).