Proposition 2 1/2 includes a provision to allow communities to increase taxes more than 2.5% when there is a need to do so. This process is known as an override. To override the 2.5% limit, the City Council or Select Board must vote to place a question on a ballot. The question includes the dollar amount of the override. It can be in the form of a menu of choices, each with a dollar amount, allowing voters to choose the particular items they support and reject others. A positive majority vote of the community is required to pass an override. When an override passes, the dollar amount specified is added to the levy limit. The new levy limit can increase 2.5% a year going forward. For example, if a community has a levy limit of 100 million dollars and an override of 5 million dollars is passed, the new levy limit is 105 million dollars. The next year the levy limit can increase 2.625 million dollars. If the override fails, the levy limit remains at 100 million and the following year it can only increase 2.5 million.
You can find more information about the provisions of Proposition 2.5 here.
Since 1988, there have been 6,064 override votes, of which 2,838 (47%) have been successful.