# Hybrid Collision Avoidance for ASVs Compliant with COLREGs Rules 8 and 13-17

## TL;DR

This paper introduces a three-layered hybrid collision avoidance system for autonomous surface vehicles that complies with COLREGs rules 8 and 13-17, effectively managing multiple obstacles and emergency situations through advanced planning and control algorithms.

## Contribution

The paper develops a mid-level COLAV algorithm that complies with COLREGs rules 13-17, integrating a new obstacle classification state machine and enhancing existing algorithms.

## Key findings

- System successfully avoids collisions in all tested scenarios.
- Maintains energy-optimized trajectory when no obstacles interfere.
- Handles multi-obstacle situations with multiple active COLREGs rules.

## Abstract

This paper presents a three-layered hybrid collision avoidance (COLAV) system for autonomous surface vehicles, compliant with rules 8 and 13-17 of the International Regulations for Preventing Collisions at Sea (COLREGs). The COLAV system consists of a high-level planner producing an energy-optimized trajectory, a model predictive control based mid-level COLAV algorithm considering moving obstacles and the COLREGs, and the branching-course model predictive control algorithm for short-term COLAV handling emergency situations in accordance with the COLREGs. Previously developed algorithms by the authors are used for the high-level planner and short-term COLAV, while we in this paper further develop the mid-level algorithm to make it comply with COLREGs rules 13-17. This includes developing a state machine for classifying obstacle vessels using a combination of the geometrical situation, the distance and time to the closest point of approach (CPA) and a new CPA-like measure. The performance of the hybrid COLAV system is tested through numerical simulations for three scenarios representing a range of different challenges, including multi-obstacle situations with multiple simultaneously active COLREGs rules, and also obstacles ignoring the COLREGs. The COLAV system avoids collision in all the scenarios, and follows the energy-optimized trajectory when the obstacles do not interfere with it.