The Field of Safe Motion: Operationalizing Affordances in the Field of Safe Travel Using Reachability Analysis

2026-04-29

AI Summary

This study addresses the lack of a computable, quantitative model for assessing whether drivers consistently maintain a collision-free escape path. It presents the first computational realization of the nearly 90-year-old Field of Safe Travel (FST) theory, which has long remained conceptual. By integrating kinematic-model-based reachability analysis, the work establishes an interpretable safety assessment framework with minimal modeling assumptions. The proposed method combines road user behavior prediction with uncertainty-bound estimation to effectively determine, across diverse traffic scenarios, whether a driver retains a feasible space of evasive actions. This yields a principled, transparent tool for quantifying driving safety that explicitly accounts for and delineates future state uncertainties.

Abstract

We present the Field of Safe Motion (FSM), a quantitative safety model for determining whether a driver maintains a collision-free escape route, or "out," at any given moment by accounting for that driver's physical capabilities and the foreseeable actions of other road users. The Field of Safe Travel (FST) provides a framework for representing the types of sensory information and actions available to drivers. However, the FST has remained conceptual in nature since its initial publication almost 90 years ago -- and a concrete computational operationalization is still lacking. At the same time, reachability analysis provides a quantitative basis for assessing the possible actions available to road users, using interpretable kinematic models, but reachability models have so far remained confined largely to the engineering and robotics literature. Bringing these two approaches together provides for an interpretable, quantitative tool for assessing driving behavior across a wide range of driving scenarios. Beyond being interpretable, our approach relies on a relatively small set of basic assumptions that are easy to enumerate and reason about. Furthermore, an interpretable reachability model paired with kinematic assumptions provides a way to bound uncertainty about road users' reasonably foreseeable future locations. We demonstrate the applicability of the FSM to different driving scenarios and discuss the strengths and weaknesses of the model.

Problem

• Field of Safe Travel
• reachability analysis
• safe motion
• driving safety
• computational operationalization

Innovation

• Field of Safe Motion
• reachability analysis
• affordances
• kinematic models
• interpretable safety model