NEXICA: Discovering Road Traffic Causality (Extended arXiv Version)

TL;DR

NEXICA is a novel causal discovery algorithm that analyzes traffic speed time series to identify highway segments that cause slowdowns, improving accuracy and speed over existing methods.

Contribution

The paper introduces NEXICA, a new approach focusing on event presence, probabilistic modeling, and binary classification for traffic causality detection.

Findings

Outperforms state-of-the-art baselines in accuracy

Faster computation on large-scale traffic data

Effective in identifying causal highway segments

Abstract

Road traffic congestion is a persistent problem. Focusing resources on the causes of congestion is a potentially efficient strategy for reducing slowdowns. We present NEXICA, an algorithm to discover which parts of the highway system tend to cause slowdowns on other parts of the highway. We use time series of road speeds as inputs to our causal discovery algorithm. Finding other algorithms inadequate, we develop a new approach that is novel in three ways. First, it concentrates on just the presence or absence of events in the time series, where an event indicates the temporal beginning of a traffic slowdown. Second, we develop a probabilistic model using maximum likelihood estimation to compute the probabilities of spontaneous and caused slowdowns between two locations on the highway. Third, we train a binary classifier to identify pairs of cause/effect locations trained on pairs of road locations where we are reasonably certain a priori of their causal connections, both positive and negative. We test our approach on six months of road speed data from 195 different highway speed sensors in the Los Angeles area, showing that our approach is superior to state-of-the-art baselines in both accuracy and computation speed.