If streets or utilities are not available at the boundary of a proposed subdivision, and if the City Planning Commission finds the extensions across undeveloped areas would not be warranted as a special assessment to the intervening properties, or as a Municipal expense until some future time, the subdivider may be required, prior to approval of the final plat, to obtain necessary easements or rights of way and to construct and pay for such extensions. Such improvements shall be available for connections by subdividers of adjoining land.