Estimation of critical gaps in two major streams

Different authors have presented capacity formulas for the case of more than one major lane when the lanes are not superposed. It has been shown that the allocation of the major flow on to the different lanes and different critical gaps for the major lanes have a substantial effect on the capacity for a minor lane. In this paper a maximum likelihood method for estimating the different critical gaps for the case of two major lanes is presented. The method can handle possible linear correlation between the critical gaps for the two major lanes. It is tested on simulated data and then applied on real data. It is then shown that the critical gaps differ between the two major lanes. The correlation coefficient was estimated for some of the subsets but for most of the subsets it was not possible to estimate.

Surrogate Measures of Safety at Roundabouts in AIMSUN and VISSIM Environment

This paper addresses issues on road safety analysis through microscopic traffic simulation models. The Surrogate Safety Assessment Model (SSAM) was applied to read vehicle trajectory files generated by two microsimulators and then calculate surrogate measures of safety. Since safety assessment of any road entity can provide different results based on the microsimulator which is used, the main objective of this research was to estimate the safety performance of three roundabout layouts and compare the conflict events simulated by AIMSUN and VISSIM. The two micro-simulators were used to build the calibrated models of the roundabouts, each fitting the corresponding empirical capacity function. The results provided insights on how to set the SSAM filters in order to have a comparable frequency of conflicts by simulation and examine conditions under which a safety analysis could be independent of the software used