Well the train, as they say, has apparently left the station.

Mayor Mufi Hannemann is well aware that a successful launch of his proposed rail transit project is key to his dream of being elected governor. If the project falters and blame cannot be clearly placed somewhere else, Hannemann will have a difficult time explaining why he should quit being mayor and instead take over the governor's office.

To be sure, Hannemann already has a talking point on why it makes sense for him to move on. It takes, he likes to say, a mayor to start a project this big. It takes a governor to finish it.

What this means is that once the project is under way, it is critical to have a governor on board to watch over financing, lobby Washington for continued support and so forth.

All this helps explain why the city is pushing ahead to break ground on the project, even as various constituency groups (environmentalists, the city auditor, some local architects, the Kamehameha Schools, even the federal courts) are raising questions. And fair enough: If the city waited until everyone was happy, the project would never be built.

So even as the complaints and doubts persist, the Hannemann administration pushes forward. Remarkably, it was able to announce the granting of the first construction contract: $482.9 million to Kiewit Pacific Co. for the first 6.5 miles of the line, ahead of schedule and $90 million under the proposed budget.

This looks good, although the start will be almost entirely symbolic. The first section would run between Kapolei and a station near — but not at — Leeward Community College. You can bet there aren't that many people making that commute today who would love to switch to rail.

Truth is, if there is one place on Oahu one can drive to and expect to find parking, it is Leeward Community College, which boasts a vast open parking space.

The real point of rushing this first segment forward is to set things in motion so there can be no turning back. Even people opposed to the project are likely to agree that once nearly half a billion has been committed, there is no other course but to go ahead and finish the thing.

The day will come when it is obvious that Honolulu — crammed into a narrow urbanized corridor between sea and mountains — will need a system of mass transit. The best argument for building now is that the effort will never be cheaper.

The worst argument for building now is that we are doing it out of political necessity. The system will be long built before we know which argument makes the most sense.