; (2) in subsection (b), in the first sentence, by inserting and subsection (c) of this section after section 419 ; and (3) by adding at the end the following: (c) Subsections (a) and (b) shall not apply to any person at least 18 years of age who distributes medicinal marihuana to a person under 21 years of age in compliance with section 710. . 5. Comptroller General study on effects of marihuana legalization on traffic safety (a) In general The Comptroller General of the United States shall conduct a study on the effects of marihuana legalization on traffic safety. (b) Inclusions The study conducted under subsection (a) shall include a detailed assessment of— (1) traffic crashes, fatalities, and injuries in States that have legalized marihuana use, including whether States are able to accurately evaluate marihuana impairment in those incidents; (2) actions taken by the States referred to in paragraph (1) to address marihuana-impaired driving, including any challenges faced in addressing marihuana-impaired driving; (3) testing standards used by the States referred to in paragraph (1) to evaluate marihuana impairment in traffic crashes, fatalities, and injuries, including any scientific methods used to determine impairment and analyze data; and (4) Federal initiatives aiming to assist States that have legalized marihuana with traffic safety, including recommendations for policies and programs to be carried out by the National Highway Traffic Safety Administration. (c) Report Not later than 1 year after the date of enactment of this Act, the Comptroller General of the United States shall submit to the appropriate committees of Congress a report on the results of the study conducted under subsection (a). 6. Rule of construction (a) In general Conduct in compliance with this Act and the amendments made by this Act— (1) shall not be unlawful; (2) shall not constitute trafficking in a controlled substance under section 401 of the Controlled Substances Act ( 21 U.S.C. 841 ) or any other provision of law