Electoral rules may be boring, but Tuesday's D.C. Council election saw them fail. While Congress designed the District's system to let voters in the minority elect a winner, it misfired on Nov. 4. Now that the council is effectively single-party, it's time to implement a system that guarantees the intended outcome.

Since 1973, the home-rule provisions have called for limited nominations to four at-large seats elected two at a time. In order to give the opposition a voice in city government, Congress forbade any party from nominating more than one candidate to these seats at the same election. While Democrats easily win each of eight single-member wards, Republicans, Greens and independents have sought representation in the at-large seats.

Until Tuesday, the system worked relatively well. Republican Carol Schwartz and David Catania, a Republican-turned-independent, were non-Democratic voices on council. True independents and the D.C. Statehood Party moreover had made gains.

But this minority representation system breaks down when opposition voters do not coordinate on a single candidate and a popular majority-party candidate runs for the same seat.

Kwame Brown handily won the Democratic at-large seat, and Michael Brown won the seat reserved to everyone else. Yet, Mr. Brown is really a Democrat; he ran as one for mayor and council in 2006 and 2007, respectively.

Going by preliminary results, Republicans split their vote to their detriment. Patrick Mara and Carol Schwartz, his incumbent write-in challenger, won a combined 21.6 percent. Mr. Brown, who ran as an independent, won with 19.9 percent of votes.

By one interpretation, Mrs. Schwartz was a spoiler. Had she accepted primary defeat and not mounted a vigorous write-in campaign, her 11 percent would have put Mr. Mara over the top, with 10.6 percent of his own. A similar interpretation might say the same about Mr. Mara: By challenging a popular Republican incumbent, he imperiled the minority. A third interpretation focuses on the winner-take-all character of the District's ostensible minority representation provisions. Because an at-large seat goes to whichever candidate wins the most votes, it was a matter of time before a Democrat used strength in numbers to win the independent seat. Republican vote-splitting meant that time was now.

As recent Wall Street events teach us, lack of regulation breeds speculation.

If the District's electoral rules translated political diversity into fair shares of the 13-member council, Democrats would hold a healthy majority, but Republicans typically would win one or two seats. The Statehood Greens or Libertarians might also win, and diversity in the Democratic Party would find fuller expression. A system that reduced the impact of spoilers and awarded seats in proportion to votes would let voters support their favorites, not force them to pick among front-runners.

That system, called proportional representation, guarantees the outcome that the District's limited nomination rule failed to deliver on Nov. 4. The proportional representation system comes in many forms. One style gaining popularity for local elections is called choice voting. Two dozen cities used choice voting during the Progressive Era, and Cambridge, Mass., still uses it today. New Yorkers elected their school board with choice voting until 2002. Minneapolis passed choice voting for some offices in 2006, and Cincinnati almost restored it Tuesday for city council elections.

Choice voting lets groups win numbers of seats equal to their strength in the electorate. At the same time, it lets voters choose candidates, not parties, so elected officials are accountable to people, not party bosses. Finally, if someone's favorite candidate doesn't win enough votes for a seat, the voter can pick someone to get his or her vote instead - no spoilers.

How does it work? Voters rank candidates in order of preference, and machines count up all the first choices. The number of votes it takes to win, a victory threshold, depends on the number of seats. Votes for winning candidates beyond the threshold count for voters' next choices. Likewise with votes for losing candidates below the threshold.

The District could use choice voting for any number of council seats. By increasing the number of at-large seats, it could preserve the current wards. If it wanted, the city could even use choice voting to eliminate expensive, low-turnout primaries as New York did in the 1930s and '40s.

Voters would rank candidates on a single election day, candidates would indicate their parties on the ballot, and the parties' strongest players would rise to the top.

If D.C. voters had used choice voting on Nov. 4, Mrs. Schwartz or Mr. Mara likely would have won a seat. Republican, Green and independent voters moreover would not have faced a zero-sum battle for it. One-party rule would not have been the outcome.

Well intentioned as it was, the limited nomination rule could not prevent that. It's time for Congress and the city alike to consider a more effective system.

Rob Richie is executive director at FairVote. Jack Santucci is a former staff member of FairVote Staff.