Abstract: based on the principles of geometrical acousties and the superposition of important early reflected sound energy on direct sound energy, a computer model which considers the containment effects associated with basically unbroken facades paraller and adjacent to a street is given in this paper. The formulae deciding the orders of important early reflected sound rays which are dependent on the heights of buildings and the distances between facades and lanes are derived. The formulae of the early reflected sound ray's length are also derived. This paper also gives another computer simulation method having the aid of scale map of street and nearby buildings which can be used for predicting the noise levels of penetration through a gap in between rows of houses perpendicular to the street.