The developer shall submit to the Approving Authority, prior to the granting of final approval, a written instrument from each serving utility which shall evidence full compliance or intended full compliance with the provisions of this section, provided, however, lots which abut existing streets where overhead electric or telephone distribution supply lines and service connections have heretofore been installed may be supplied with electric and telephone service from those overhead lines shall be installed underground. In the case of existing overhead utilities, should a road widening or an extension of service or other such condition occur as a result of the development and necessitate the replacement, relocation or extension of such utilities, such replacement, relocation or extension shall be underground.