396 Determination of optimal segment length for road crash analysis using power spectral analysis

<h3>Background</h3> Roadway segmentation is a fundamental step in crash frequency model estimation and evaluating engineering interventions before and after. The road segment selection is usually conditioned to specific attributes and objectives of safety analysis. Further, the existing segmentation methods depend on subjective decision-making theory and lack standardised metrics for evaluating segment length performance in modelling. <h3>Objective</h3> This study describes a data-driven analytics-based roadway segmentation approach to ascertain an optimal segment length (OSL) for safety performance assessment. <h3>Methodology</h3> The study methodology used a redesigned spectral analysis approach based on the spatial frequency domain (SFD) framework for roadway segmentation. This redesigned SFD-based approach is presumed to follow a hypothesis that crash density sequence (CDS) along a road has major power spectral concentration in low-frequency bands. Furthermore, the Nyquist-Shannon sampling theorem suggests that the OSL or Power Spectral Segment Length (PSSL) can be approximated by the upper limit of the low-frequency band that contains major power in the power spectral density (PSD) of the CDSs. <h3>Results</h3> The PSSL performance metrics (power spectral percentage (PSP) and PSD) validate the hypothesis that CDS along a road has major power concentrated in low-frequency bands. The two highways (NH 334B S2 and SH 16A) have 78.86% to 86.27% of PSP concentrated in the 0–0.4 S-Hz/0–0.5 S-Hz band. Whereas the other four highways (NH 334B S1, NH 709, SH14, and SH22) have 67.85% - 78.72% of PSP in 0–0.3 S-Hz/0–0.7 S-Hz band. Thus, the two highways with 78.86% to 86.27% of PSP concentrated in low-frequency bands had lower PSSL or OSL ranging from 126 m to 144 m. Similarly, it ranges from 185 m to 245 m for the other four highways. <h3>Conclusion</h3> This study used a redesigned spectral analysis approach based on the spatial frequency domain (SFD) framework to determine the OSL for six different highways. Interestingly, all six highways have different OSLs ranging from 126 to 245 m. Thus, a fixed-length segment cannot be optimal for every highway alignment. <h3>Future Scope</h3> In the future study, the authors will investigate the performance of the OSL in developing safety performance functions.