If Cayetano wins the mayoral election over pro-rail candidate Kirk Caldwell, the city's former managing director, that could be seen by some on the council as a referendum to kill the project.

"If Gov. Cayetano is successful, I mean we cannot ignore that fact," said Martin. "The outcome of the general election will have some impact in terms of where we're headed in the next few years."

In December 2010, Berg won his Council District 1 seat with 2,326 votes in a field that contained 14 candidates. The special election to fill Gabbard's seat could be just as crowded.

Former Honolulu City Councilman Jon Yoshimura, who served Council District 6 from 1995 to 2002, has said he will run for Gabbard's seat. Yoshimura would not say whether he supports the rail project when contacted by KITV4, but said he would address the issue Friday when he official announces his candidacy.

Others that have expressed interest in serving the remainder of Gabbard's term include State Sen. Carol Fukunaga, former Hawaii GOP chairman Sam Aiona, the city's director of Information Technology Gordon Bruce, and state representatives Karl Rhoads, and John Mizuno.

Martin said Gabbard’s vacancy would be announced during a special hearing of the City Council on Aug. 22. That will make the beginning of the official 10 day filing period for potential candidates.

“I anticipate that we might get up to a dozen candidates to enter this particular race,” said Martin.

Gabbard, the Democratic candidate for Hawaii’s Second Congressional District, decided to step down from the Council immediately to save city taxpayers as much as $150,000, the estimated cost of holding a special election. She insists she’s not overlooking her Republican challenger in the general election, Kawika Crowley, of Hilo.

“Today really is about what is best for my constituents of Council District 6, and making sure that the taxpayers of the City and County of Honolulu don't have any added extra costs for any special election,” said Gabbard.

Gabbard beat former Honolulu Mayor Mufi Hannemann in the Aug. 11 Democratic primary 54 percent to 33.6 percent.