Cycling safety assessment in microscopic traffic simulation: A review and methodological framework

Abstract

Vulnerable road user safety is paramount for increasing shares of active travel modes and introducing automated vehicles. Microscopic traffic simulation is a prevalent method in research and practice with a growing focus on safety and cyclists. Its practical benefits make it an essential tool for developing safe future transportation. We review the methodology of simulation studies and the validation of their microscopic models to evaluate cycling safety assessment in microscopic simulations. We find that current work relies predominantly on the lane-based models of established traffic flow simulation packages that separate longitudinal and lateral dynamics. These models do not sufficiently capture diverse behaviors and conflict causality to predict cycling safety. In contrast, new models with successful calibrations and validations advance simulated interactions towards capturing conflict causality. Of 42 reviewed studies, six calibrate, and three validate models for safety prediction. Other studies disregard calibration and validation, posing a threat of unfounded safety predictions and unsafe design recommendations. We present a methodological framework conceptualizing best practices for reliable assessment. It calls for the identification of safety-relevant behaviors of cyclists and other road users in conflicts. Specialized behavioral models must be developed, calibrated, and validated. The selected safety indicators must enable capturing the expected unsafe events. To create these tools, improved models of cycling behavior must be transferred to established simulation packages. Following the framework, researchers and practitioners can use simulation as a practical and ethical means to assess the cycling safety impact of innovations ranging from infrastructure to automation and connectivity.