Propose/enact Federal legislation that the Secretary of Transportation shall withhold 20 per cent of the amount required to be apportioned to any State under the Federal Aid Highway Act, beginning after September 30, 2013, in which the purchase or public possession in such State of marijuana (or any other Federally criminalized/prohibited drug) is lawful.
This is similar to the National Minimum Drinking Age Act of 1984, which encouraged States to enact and enforce a minimum drinking age of 21. If the Federal government chooses to not enforce Federal law prohibiting the possession or purchase of marijuana through law enforcement means, encourage the States to act responsibly and enforce it. States like CO, WA, CA etc., can make a choice -- weed or highway funds. Protect our children!