Driving Safety-Volatility-Emissions integrated indicator-application to urban road environment

Understanding driver behaviour, particularly identifying critical safety distances or anomalous driving patterns, is essential to improve road safety and mitigate pollutant emissions, especially in urban areas. The development of indicators that include safety, volatility, and emissions for assessing driver performance in urban environments is scarce. The goal of this research is to develop an integrated driving indicator (iDI) that accurately assesses driver behaviour based on second-by-second data relative to safety (time headway and stopping distance), volatility (acceleration and vehicular jerk), and emissions (carbon dioxide and nitrogen oxides) variables. For that purpose, an optimisation problem was formulated, and a sensitivity analysis was conducted on the above parameters to estimate the best weights on each factor. An urban case study near a university campus in Central Region, Portugal, composed of two roundabouts, one signalised, and one stop-controlled intersection, was selected to evaluate the iDI performance. Simulations were conducted using the microscopic traffic simulation model VISSIM, where both vehicle record and trajectory data were exported. The latter was used in the Surrogate Safety Assessment Model to evaluate traffic conflicts and then, the results were correlated with the developed iDI. Light-duty vehicles were identified as the primary participants in most conflicts, comprising at least 96% of incidents during each demand period. Despite representing over 72% of the total fleet, these vehicles demonstrated iDI scores ranging from 20% to 30%. Results suggest that volatility and emissions are relevant factors significantly contributing to the integrated driving score. The components in the driving performance indicator include vehicle variables that have an impact on both accidents and gas emissions. They are suitable for assessing driving behaviour and promoting greater driver responsibility.