This chapter shall not apply to permanent buildings, public utility poles; trees trimmed to the trunk to a line at least eight feet above the level of the street pavement or roadway surface; saplings or plant species of open growth habits and not planted in the form of a hedge, which are so planted and trimmed as to leave at all seasons a clear and unobstructed crossview; supporting members of appurtenances to permanent buildings existing on the effective date of this title; official traffic control signs, poles, or signals; or to places where the contour of the ground is such that there can be no cross-visibility at the intersection.