; and (2) mobility on demand services. (b) Federal share (1) In general Except as provided in paragraphs (2), (3), and (4), the Federal share of the net cost of a project carried out under this section shall not exceed 80 percent. (2) Mobility on demand service operating costs The Federal share of the net cost of a project to provide for net operating costs for mobility on demand services shall not exceed 50 percent for any funds provided under section 5307. (3) Mobility as a service cost share Notwithstanding paragraph (1), the Federal share of the net cost of mobility as a service shall not exceed 90 percent. (4) Zero emission incentive Notwithstanding paragraphs (1) and (2), the Federal share of the net cost of a project described in paragraph (1) or (2) shall be reduced by 25 percent if such project involves an eligible use that uses a vehicle that produces carbon dioxide or particulate matter. (c) Eligible uses (1) In general The Secretary shall publish guidance describing eligible activities that are reasonably expected to— (A) increase transit ridership; (B) be complementary to fixed route transit service; and (C) demonstrate substantial improvements in— (i) environmental metrics, including standards established pursuant to the Clean Air Act ( 42 U.S.C. 7401 et seq.) and greenhouse gas performance targets established pursuant to section 150(d) of title 23; (ii) traffic congestion; (iii) compliance with the requirements under the Americans with Disabilities Act of 1990 ( 42 U.S.C. 12101 et seq.); (iv) low-income service to increase access to employment, healthcare, and other essential services; (v) service outside of transit agency operating hours; (vi) low density service