As a graduate student I was perplexed by the number of arrests made for driving under the influence of alcohol at the bars and pubs near my University. I did a bit of research and it turned out the biggest effort for reducing drinking and driving was having no real impact on behaviour. Government agencies in the USA were spending tens of millions of dollars on an advertisement campaign warning people of the dangers of drinking and driving, yet the number of arrests was actually increasing.
I decided to try something new in my hometown. First, I convinced local breweries to give me money, which I then used to incentivise college students for being more responsible. I located a breathalyser,donated by the local police department, to measure the blood alcohol content of students out at the pubs. I advertised that anyone who had with them another person capable of proving they've consumed no alcohol when leaving would receive free pizza and money towards fuel purchase. It was easy - simply provide a breath sample, register a 0.0 BAC and you win.
As a result the overall percentage of students using designated drivers increased from near 0% to 25% and number of arrests dropped in the community.