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LaneChange Model

Goals

Our goal is to refactor Plexe within SUMO in order to:

  • Ensure that isolated Plexe vehicles behave exactly like native SUMO vehicles, correctly adopting a native SUMO car-following model (EIDM, Krauss, ACC, …) and, especially, take exactly the same LaneChange actions.
  • Introduce a collective LaneChangeModel for vehicles that are part of a platoon, so that lane change maneuvers are coordinated and safe.

This way we can achieve realism for isolated vehicles and consistent behavior for platoons.

Introduction

Currently, Plexe vehicles suffer from several issues:

  • When isolated, they still rely on MSCFModel_CC and related overrides which do not mimic realistic human behavior (too aggressive or unmotivated lane changes).
  • laneChangeMode bits are disabled to accommodate short gaps of followers, with the side effect that even leaders or isolated vehicles lack proper safety logic.
  • There is no clear separation between car-following models (longitudinal) and lane-changing models (lateral). For example, autolaneChange is currently implemented at the Cruise Controller (car-follow-model) side.

These limitations motivate a refactoring that makes Plexe behavior more modular, realistic, and maintainable.

Refactoring Idea

The refactoring introduces:

  • A PlexeVehicle class extending MSVehicle and holding dynamic references to:
    • active_cfmodel → one among EIDM, Krauss, ACC, MSCFModel_CC
    • active_lcmodel → either LC2013 (isolated) or PlexeLCModel (collective).
  • The possibility to switch car-following models at runtime through dedicated APIs (e.g., plexe.setActiveCFModel(vehID, "EIDM")).
  • A collective LaneChangeModel where:
    • The leader evaluates its lane change decision.
    • If willing to change, it checks that no follower is blocked.
    • If all are free, the whole platoon changes lane simultaneously.
    • If even a single follower is blocked, the maneuver is aborted for everyone.

UML Sketch

Test

The following tests (implemted by examples/lanechange_tests.pyhttps://tests.ing.unibs.it/ghiro/plexe-pyapi/-/blob/sumo1.24_lanechange_refactoring/examples/lanechange_tests.py on the sumo1.24_lanechange_refactoring dev-branch) are designed to validate the new design. Each case has a User Story (expected behavior from the user’s perspective) and a Refactor Story (how the refactored code ensures the outcome).

Test Case User Story Refactor Story Expected Outcome
1 – Native SUMO SUMO vehicles with EIDM, Krauss, and ACC (cases 1A, 2A, 3A). On a 3-lane highway with a slow car 200m ahead and an exit further ahead, each model overtakes and takes the exit according to its own style. Baseline reference: SUMO native implementation of EIDM, Krauss, and ACC. Each model shows its expected style: EIDM regular overtakes, Krauss more variable (σ), ACC smoother and more conservative.
2 – Plexe Isolated Isolated Plexe vehicle with active_cfmodel = EIDM / Krauss / ACC (cases 1B, 2B, 3B). Scenario identical to Test 1. PlexeVehicle delegates to the corresponding MSCFModel_* (EIDM, Krauss, ACC) and uses LC2013 for lane changes. Identical behavior to Test 1. No observable difference between Plexe and SUMO native vehicles with the same CF model.
3 – Plexe Switching Single-lane road, slow vehicle ahead. A Plexe vehicle switches every 10s between EIDM, Krauss, and ACC. All three CFModels are instantiated at birth and continuously updated. Switching is a pointer reassignment. Smooth transitions without discontinuities. Driving style changes at runtime according to the active model.
4 – Platoon Collective A platoon of 4 vehicles is present from the start. The leader can be: (a) a SUMO native (EIDM, Krauss, ACC), or (b) a Plexe leader using Plexe_CC. Followers are Plexe vehicles with CACC or PLOEG. The platoon approaches a slow vehicle, overtakes collectively, returns to the right only once all members have cleared the slow vehicle, and finally all take the exit together. PlexeLCModel handles collective lane change: leader decides, followers report blocked/unblocked state. Maneuver only proceeds if all are free; otherwise aborted. Followers delegate longitudinal control to their CF model (CACC or PLOEG). The platoon behaves as a single unit: overtakes as a block, shifts back to the right once fully clear, and exits together. Individual followers never attempt independent lane changes.