The way our democracy is set up citizens have no control over things like that. There was never a vote to make the legal drinking age 21.
As far as drunk driving.
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There were no vote, but if you can prove that there should be one, you can get one. If someone collects more than x signatures (problably varies from country to country), any law shall be voted for by the entire country.
But here in Denmark, there are made several thousand laws and law adjustments every year, and it is so much, that we've hired some people called politicians to spend all their day reading rapports and choosing laws, so we can be at work instead of the voting booth for our entire life.
And you know the best part are? We've chosen those politicians ourself, and opposite from usa, we've got many parties to choose from, and many politicians from every party, so practically we have kinda fair control over what laws are passed.
Example: 2010-11 we had a law, that 14 year olds could go to jail. Despite that the law were only used 4 times during the year it was active, the danish citizens hated the law so much, that it have been changed back to 15 and since then, we've got a new government, where the party that wanted the criminal age down at 14 are not in anymore, due to lack of votes.
Democracy from the socialistic scandinavia!