PMA-Diffusion: A Physics-guided Mask-Aware Diffusion Framework for TSE from Sparse Observations

TL;DR

PMA-Diffusion is a physics-guided, mask-aware diffusion framework that effectively reconstructs high-resolution highway traffic speed fields from sparse, noisy observations, outperforming baselines even at 5% visibility.

Contribution

The paper introduces a novel physics-guided mask-aware diffusion approach for traffic state estimation from sparse data, with specialized training strategies and a physics-based posterior sampler.

Findings

Outperforms baselines at 5% visibility ratio

Nearly matches fully observed model performance when trained on sparse data

Effective in reconstructing detailed traffic speed fields from limited observations

Abstract

High-resolution highway traffic state information is essential for Intelligent Transportation Systems, but typical traffic data acquired from loop detectors and probe vehicles are often too sparse and noisy to capture the detailed dynamics of traffic flow. We propose PMA-Diffusion, a physics-guided mask-aware diffusion framework that reconstructs unobserved highway speed fields from sparse, incomplete observations. Our approach trains a diffusion prior directly on sparsely observed speed fields using two mask-aware training strategies: Single-Mask and Double-Mask. At the inference phase, the physics-guided posterior sampler alternates reverse-diffusion updates, observation projection, and physics-guided projection based on adaptive anisotropic smoothing to reconstruct the missing speed fields. The proposed framework is tested on the I-24 MOTION dataset with varying visibility ratios. Even under severe sparsity, with only 5% visibility, PMA-Diffusion outperforms other baselines across three reconstruction error metrics. Furthermore, PMA-diffusion trained with sparse observation nearly matches the performance of the baseline model trained on fully observed speed fields. The results indicate that combining mask-aware diffusion priors with a physics-guided posterior sampler provides a reliable and flexible solution for traffic state estimation under realistic sensing sparsity.