The aim of the paper is to present the results of a study about involving the human error into traffic modeling. The analysis of driver's behavior in a selected traffic situation (drivers do or do not stop at red light) provided us to define the meaning human error in the context. Based on Bayesian theorem, the probability of bad decision is one of the results of the first part of this paper. Having built the junctions in VISSIM environment, and after a detailed investigation of output parameters (in simulated traffic there is no car passing at red), a software module was developed for having the bad decision probabilities using VISSIM. Grouping drivers by driving style (aggressive, normal, slow) gives opportunity (defining numbers of driver passing at red) to find the missing link. The trial version of this software now is able to define the probability of bad decision using VISSIM outputs.