(a) General rule.--The department shall distribute highway appropriations and executive authorizations for State highway maintenance in the various county maintenance districts in the following manner:

(b) Formula for distribution.--The department shall distribute to each county maintenance district:

(c) Establishment of applicable data.--The applicable data for all counties corresponding to each individual factor in the incremental formula in subsection (b) shall be established and certified by the Governor by May 1 of each year based on the best information available at that time for the immediately preceding five-year period with the exception of BMD. The submission of data relative to BMD shall only include the immediately preceding 12-month period beginning with fiscal year 1997-1998. In each subsequent fiscal year, an additional year of data relative to BMD shall be added until such time as data from a five-year period has been accumulated.

(d) Effect of insufficient funds.--In the event sufficient funds are not available to fully fund all county maintenance districts under the formula in subsection (b) due to the hold harmless provision in subsection (a), each county maintenance district receiving an increase above its base allocation shall have its share reduced in the proportion that the increase over its base allocation bears to the total increases over the base allocation of all counties entitled to an increase, to the extent necessary to bring the total allocations within the funding limit.