Streets in the subdivision or land development of sufficient width and suitable grade and suitably located to accommodate prospective traffic and to provide access for firefighting and emergency equipment to buildings and coordinated so as to compose a convenient system consistent with the official map, if any, and the circulation element of the master plan, if any, and so oriented as to permit, consistent with the reasonable utilization of land, the buildings constructed thereon to maximize solar gain; provided that no street of a width greater than 50 feet within the right-of-way lines shall be required unless said street constitutes an extension of an existing street of the greater width, or already has been shown on the master plan at the greater width, or already has been shown in greater width on the official map;