The width of any proposed lot shall not be less than set forth in Schedule B[1] or the average width of the lots on each side of the street the lot is located, within 500 feet of the exact midpoint of the lot, measured from the midpoint of the lot along the centerline of the street upon which the lot fronts on, whichever is greater. When computing the average width of the surrounding lots, the following lots shall be excluded from the computation: the lot to be subdivided, lots which have been vacant more than five years and lots containing conforming nonresidential or multi-family uses.