Policy Library CBF: Finite-Horizon Safety at Runtime via Parallel Rollouts

2026-05-15

AI Summary

This work addresses the challenge of runtime safety certification under dynamic constraints in unstructured environments by proposing a Policy Library Control Barrier Function (PL-CBF) framework. The approach establishes a finite-horizon rollback mechanism that operates multiple policies in parallel, leverages language metric theory to formally characterize policy library coverage conditions, and employs quadratic programming to minimally modify a nominal policy by selecting the least intrusive safe mode. Experimental evaluations on double integrator systems, nonlinear vehicle models, and 3D quadrotor platforms demonstrate that PL-CBF substantially outperforms conventional single-policy filtering methods, achieving higher safety coverage while maintaining millisecond-level computational efficiency.

Abstract

Safety-critical autonomy in unstructured environments poses significant challenges for online safety certification under evolving constraints. We propose Policy Library Control Barrier Function~(PL-CBF), a runtime safety filter that evaluates a library of fallback policies via parallel finite-horizon rollouts, selects the least invasive safe mode, and enforces safety by solving a quadratic program that minimally modifies a nominal policy. We provide a theoretical analysis based on a finite-horizon language metric over closed-loop behaviors, characterizing policy-library coverage requirements for certifying finite-horizon safety. Simulations on a planar double-integrator (4 states), highway driving with abrupt friction changes using a realistic nonlinear vehicle model (8 states), and 3D quadrotor navigation in crowded dynamic environments (12 states) demonstrate improved safety coverage over single-policy safety filters while retaining millisecond-level runtime.

Problem

• runtime safety certification
• finite-horizon safety
• unstructured environments
• evolving constraints
• safety-critical autonomy

Innovation

• Policy Library CBF
• finite-horizon safety
• parallel rollouts
• runtime safety filter
• quadratic program