For street widening, alignment, corrections, channelization of intersections, construction of barriers, new or improved traffic signalization, signs, curbs, sidewalks, trees, utility improvements not covered elsewhere, the construction of new streets and other similar street or traffic improvements, the owner's or subdivider's proportionate cost shall be the ratio of the estimated peak-hour traffic generated by the proposed property or properties to the sum of the present deficiency in peak-hour traffic capacity of the present facility and the estimated peak-hour traffic generated by the proposed development. The ratio thus calculated shall be increased by 10% for contingencies.