Risk-Budgeted Control Framework for Balanced Performance and Safety in Autonomous Vehicles

Abstract: This paper presents a risk-budgeted monitor with a control framework that certifies safety for autonomous driving. In this process, a sliding window is proposed to monitor for insufficient barrier residuals or nonzero tail risk, ensuring system safety. When the safety margin deteriorates, it triggers switching the safety constraint from a performance-based relaxed-control barrier function (R-CBF) to a conservative conditional value at risk (CVaR-CBF) to address the safety concern. This switching is governed by two real-time triggers: Feasibility-Triggered (FT) and Quality-Triggered (QT) conditions. In the FT condition, if the R-CBF constraint becomes infeasible or yields a suboptimal solution, the risk monitor triggers the use of the CVaR constraints for the controller. In the QT condition, the risk monitor observes the safety margin of the R-CBF solution at every step, regardless of feasibility. If it falls below the safety margin, the safety filter switches to the CVaR-CBF constraints. The proposed framework is evaluated using a model predictive controller (MPC) for autonomous driving in the presence of autonomous vehicle (AV) localization noise and obstacle position uncertainties. Multiple AV-pedestrian interaction scenarios are considered, with 1,500 Monte Carlo runs conducted for all scenarios. In the most challenging setting with pedestrian detection uncertainty of 5 m, the proposed framework achieves a 94-96% success rate of not colliding with the pedestrians over 300 trials while maintaining the lowest mean cross-track error (CTE = 3.2-3.6 m) to the reference path. The reduced CTE indicates faster trajectory recovery after obstacle avoidance, demonstrating a balance between safety and performance.