The formula allocation for counties for the distribution of motor fuel tax funds, provided for in Section 8 in the “Motor Fuel Tax Law”, may be used by the county board for the maintenance or improvement of nondedicated subdivision roads established prior to July 23, 1959. Any such improved road becomes, by operation of law, a part of the township or district road system in accordance with Section 6-325 of this Code. The county board shall condition its approval, as required by this Section, upon proportional matching contributions, whether in cash, kind, services or otherwise, by property owners in the subdivision where such a road is situated. No more than the amount of the increase in allocation of such funds allocated under the formula as provided in Section 8 in the “Motor Fuel Tax Law” which is attributable to this amendatory Act of 1979 and any subsequent amendatory Act and subsequently approved as provided in this Section, may be expended on eligible nondedicated subdivision roads.