01550570

Component

The Conflict Propensity Metric (CPM) and the Aggregate Conflict Propensity Metric (ACPM) are two simulation-based conflict metrics recently proposed as surrogate safety measures. CPM is able to quantify crash probabilities of conflicts and ACPM captures relative safety levels of traffic facilities or treatments. The two metrics are derived through a stochastic process incorporating distributions of driver reaction time (RT) and vehicle maximum braking rates (MABR). This paper presents sensitivity analyses on the two metrics, by altering the parameters (i.e. mean and standard deviation) of RT distributions. Both RT mean and standard deviation affect the estimates of CPM for the three conflict types examined here (i.e. crossing, rear-end and lane change), and the impacts vary by conflict types, indicating the need of carefully evaluating and considering RT distributions and conflict types when developing simulation-based conflict metrics. A sensitivity analysis based on field data showed that different RT distributions have an impact on ACPM and could affect the reliability of ACPM in identifying relative safety as well as its correlation with actual crashes. The analysis here identified the “realistic” RT distributions for different conflict types and the suggested values are considered reasonable or consistent with prior findings. ACPM has proved to have potential to further improve its accuracy using more suitable RT distributions. However, dedicated RT distributions for different conflict types are lacking, impeding the improvement of ACPM. In general, sensitivity analyses have shown the validity of the process of deriving CPM and ACPM.

This paper was sponsored by TRB committee ANB20 Safety Data, Analysis and Evaluation.

01550057

15-2628

English

20p

2015

Transportation Research Board 94th Annual Meeting

Digital/other

Figures; References (22) ; Tables

Behavior; Braking; Drivers; Reaction time; Sensitivity analysis; Stochastic processes; Traffic conflicts

Data and Information Technology; Highways; Safety and Human Factors; I83: Accidents and the Human Factor

Transportation Research Board Annual Meeting 2015 Paper #15-2628

TRIS, TRB, ATRI

Dec 30 2014 12:54PM