Two years after Dartmouth College started a national initiative to reduce binge drinking, it says the number of its students treated for extreme alcohol intoxication has been reduced by more than half. In 2011, Dartmouth started a project with other colleges and universities that brought together campus teams to share experiences and help one another test strategies. It became known as the National College Health Improvement Program. Dartmouth’s team wanted to get rid of cases of medical interventions in which students registered a blood alcohol count greater than .25, more than three times the legal limit in New Hampshire. In the 2012-2013 school year, 31 students in that category needed medical help. That number is down from 63 the previous year and down from 80 two years ago. Dartmouth and other schools participating in the project are attending an informational session in Boston this week to share experiences.