All revenues derived from fees, excises and license taxes relating to registration, operation and use of vehicles on public highways, and to fuels used for propulsion of such vehicles shall be expended solely for cost of administration, statutory refunds and adjustments, payment of debts and liabilities incurred in construction and reconstruction of highways and bridges, the cost of construction, reconstruction, maintenance and repair of public highways and bridges under the direction and supervision of a state department having jurisdiction over such highways and bridges and expense for state enforcement of traffic laws and shall not be diverted for any purpose, provided that these limitations shall not apply to revenue from an excise tax on motor vehicles imposed in lieu of personal property tax.