Who could have predicted that, in an election season of national import, it would be the mayoral contest that, in Honolulu at least, is generating all the heat?

Former Gov. Ben Cayetano, for months a prominent figure in the ongoing court battles over the city’s planned fixed-rail project, surprised many observers when he announced this week that he is indeed running for Honolulu mayor.

It’s an unconventional step for a two-term governor, particularly one who never previously showed much interest in municipal affairs, but Cayetano has always exhibited a flair for the unconventional. Those familiar with that career history doubtlessly were surprised but probably not shocked.

He is a clearly capable campaigner of long experience and enters a field of veterans: the incumbent, Peter Carlisle, the former city prosecutor who won a partial term 18 months ago in a special election; and Kirk Caldwell, the longtime state legislator who became city managing director and then acting mayor when Mufi Hannemann stepped down from City Hall’s top post to run for governor.

Nobody disputes that Cayetano was drawn to the prospect of becoming mayor by the influence the post would give him over the future of the $5.27 billion rail project. He is an outspoken opponent and a plaintiff in a federal lawsuit seeking to block the project on the grounds that its planners did not sufficiently consider more environmentally friendly and cost-effective alternatives. Carlisle and Caldwell both stand staunchly on the side of the 20-mile transit development.

As much as this has dominated city politics, these candidates, as well as anyone else entering the race, are asking the voters for a job that will last a full, four-year term. Rail is a central, even predominant issue, but simply favoring or opposing it can’t be the sole criterion for voter judgment.

Cayetano took care to avoid at least the appearance of being a one-issue candidate in his announcement on Thursday, and he pledges next week to begin outlining his plans for a range of city projects, such as the city’s sewage and secondary treatment plant upgrades, road maintenance and other priorities.

We’ll hold him to that pledge — and expect his rivals similarly to come forward with their plans for Honolulu’s future.

The city faces enormous challenges in the coming years, not the least of which is a blueprint for managing its unfunded liabilities for its retired workforce. Balancing that responsibility against the creation of tax policy that provides adequate resources for city operations without weighing too heavily on the payers of property taxes is crucial, especially at this point in a fragile economic recovery.

Regardless of an individual candidate’s position on rail, each needs to articulate a vision on how transportation can be developed to serve the needs of Oahu residents, one that meshes well with a concept of urban growth, density and land use.

That’s what voters need to hear between now and November — not more of the same single-issue rhetoric that, up to this point, has overwhelmed all else.