; 117 Stat. 2518) is amended by striking and for the period beginning on October 1, 2015, and ending on September 30, 2017, and inserting and for fiscal years 2018 through 2021 . 1208. Airport road funding (a) Airport development grant assurances Section 47107(b) is amended by adding at the end the following: (4) This subsection does not prevent the use of airport revenue for the maintenance and improvement of the on-airport portion of a surface transportation facility providing access to an airport and non-airport locations if the surface transportation facility is owned or operated by the airport owner or operator and the use of airport revenue is prorated to airport use and limited to portions of the facility located on the airport. The Secretary shall determine the maximum percentage contribution of airport revenue toward surface transportation facility maintenance or improvement, taking into consideration the current and projected use of the surface transportation facility located on the airport for airport and non-airport purposes. The de minimus use, as determined by the Secretary, of a surface transportation facility for non-airport purposes shall not require prorating. . (b) Restrictions on the use of airport revenue Section 47133(c) is amended— (1) by inserting (1) before Nothing and indenting appropriately