The subjects and rates of taxation in the Township shall be those allowable under the Second Class Township Code of the Commonwealth of Pennsylvania on the effective date of this Charter and those allowable from time to time under general law and other laws of the Commonwealth of Pennsylvania applicable to townships of the second class except as follows:
a. 
The rate of taxation on real property for roads, bridges and general Township purposes shall not exceed 19 mills, except the Board by ordinance may increase said rate of taxation not to exceed three additional mills in the aggregate in any four consecutive years by not more than one mill per year by the affirmative vote of at least four members thereof or by not more than two mills per year by the affirmative vote of at least five of the members thereof; and
b. 
The rates of taxation on any allowable taxes may be raised above the limitations set forth in this Charter by following the referendum procedures set forth in § 409 of this Charter.