Real-time risk estimation for active road safety: Leveraging Waymo AV sensor data with hierarchical Bayesian extreme value models

TL;DR

This paper introduces a real-time risk estimation framework for near-misses in autonomous vehicle traffic, leveraging hierarchical Bayesian extreme value models and high-resolution Waymo sensor data to improve safety analysis across diverse highway conditions.

Contribution

It develops a versatile, real-time risk estimation framework using hierarchical Bayesian EVT models that incorporate vehicle dynamics and heterogeneity, applicable to various highway environments.

Findings

Risk varies significantly across conflicting vehicle pairs.

Hazardous conditions involve conflicting speeds and rapid acceleration/deceleration.

The hierarchical Bayesian model outperforms traditional methods in statistical accuracy.

Abstract

This study develops a real-time framework for estimating the risk of near-misses by using high-fidelity two-dimensional (2D) risk indicator time-to-collision (TTC), which is calculated from high-resolution data collected by autonomous vehicles (AVs). The framework utilizes extreme value theory (EVT) to derive near-miss risk based on observed TTC data. Most existing studies employ a generalized extreme value (GEV) distribution for specific sites and conflict types and often overlook individual vehicle dynamics heterogeneity. This framework is versatile across various highway geometries and can encompass vehicle dynamics and fidelity by incorporating covariates such as speed, acceleration, steering angle, and heading. This makes the risk estimation framework suitable for dynamic, real-world traffic environments. The dataset for this study is derived from Waymo perception data, encompassing six sites across three cities: San Francisco, Phoenix, and Los Angeles. Vehicle trajectory data were extracted from the dataset, and near-miss frequencies were calculated using high-fidelity 2D TTC. The crash risk was derived from observed near misses using four hierarchical Bayesian GEV models, explicitly focusing on conflicting pairs as block minima (BM), which revealed that crash risk varies across pairs.The proposed framework is efficient using a hierarchical Bayesian structure random parameter (HBSRP) model, offering superior statistical performance and flexibility by accounting for unobserved heterogeneity across sites. The study identifies and quantifies that the most hazardous conditions involve conflicting vehicle speeds and rapid acceleration and deceleration, significantly increasing crash risk in urban arterials.