Aspen City Council is working out the details of instant runoff voting, which will be in place next time Aspen voters go to the polls in May.

Instant runoff voting allows voters to rank their candidate preference, with those rankings coming into play if no one candidate gets elected based on the electorate’s first choices. The system then eliminates lower-ranked candidates, with the voter’s second choice being counted if his or her first choice is eliminated.

Council passed a plan on a preliminary vote that will likely be amended before the final vote, which could be as early as the Feb. 23 meeting. There is some confusion and debate over the method proposed for council elections, which are complex because there are two open seats and usually multiple candidates. The plan proposed would eliminate lower ranking candidates in batches, as opposed to another proposal that would eliminate candidates sequentially.

Aspen voters approved amending the city charter to institute instant runoff voting in the November 2007 election. A task force was set up to recommend the best way to implement the system. The charter amendment approved also changes the threshold required to win a council seat. In the past, a council candidate needed 45 percent of the votes to win, but the charter change raises that to a 50 percent plus one majority. The mayor election has always required a majority.

Aspen has held runoff elections one month after the first round in the event that no one candidate captured enough of the vote to win. The city has proposed eliminating the separate runoff election to eliminate the hassle of another month of campaigning and avoid the expense that comes with holding another election. In the 10 years since Aspen instituted the current runoff system, no candidate has ever won who did not have the highest vote totals in the first round.