Abstract

Safety measurement and analysis have been a challenging and well-researched topic in transportation. Conventionally, surrogate safety measures have been used as safety indicators in simulation models for safety assessment, in control formulations for driver assistance systems, and in data analysis of naturalistic driving studies. However, surrogate indicators only give partial insights into traffic safety i.e., they only indicate a predetermined set of possible pre-crash situations for an interacting vehicle pair. Recently, a safety indicator called the driving safety field based on field theory has been proposed for two-dimensional vehicle interactions. However, the objectivity of its functional form and validity are yet to be tested. This paper provides a qualitative and quantitative comparison of different safety indicators as a risk measure to demarcate their mathematical properties and evaluate their usefulness in quantifying trajectory risk. We compare five relevant safety indicators: inverse time to collision, post-encroachment time, potential indicator of collision with urgent decceleration, warning index and safety field strength. Their formulations are mathematically analyzed to yield qualitative insights and their values over simulated vehicle trajectories are evaluated to yield quantitative insights. Our results acknowledge the limitations and demarcate the functional utilities of the selected safety indicators.

Abstract

Performance of Two-way Stop-controlled (TWSC) intersections is greatly affected by the gap acceptance capabilities of drivers. However, there have been no detailed studies conducted regarding driver age differences in gap acceptance capabilities under different light conditions. Therefore, this study was conducted to fill the lack of information in that area, by considering three driver age groups (old, middle, and young), two maneuvers (left-turn, and through), and two light conditions (daytime, and nighttime). Field observations were made at several TWSC intersections and data were collected at these sites regarding available and accepted gaps on the major street and age group of minor street drivers, both during daytime and nighttime. Statistical analysis conducted in this study with a 5% level of significance revealed that there were significant differences in gap acceptance capabilities among the three driver age groups under both light conditions. Only older drivers indicated statistically different gap acceptance capabilities depending on the light condition, where they illustrated longer critical gap values during nighttime. Document type: Article