Abstract: Let R be an open equivalence relation on a topological space E. We define on E a new equivalence relation ̃︀ R by x̃︀ Ry if the closure of the R-trajectory of x is equal to the closure of the R-trajectory of y. The quotient space E/̃︀ R is called the trajectory class space. In this paper, we show that the space E/̃︀ R is a simple model of the quotient space E/R. This model can provide a f...