When the City Council takes a final vote next month on raising taxes to fund a mass-transit system for O'ahu, it might be the most momentous moment in recent city history.

No matter what happens, people will look back and see it as a pivotal point in the way Honolulu matures as a city. Indeed, it's not too strong to say that the next 50 or 100 years of Honolulu's urban planning hang in the balance as nine elected officials decide which way we are going to grow: up, or out.

For better or worse, a mass- transit system will change Honolulu forever. The full effects will take decades to be felt, but there's no doubt that ultimately we'll become a more urban — rather than suburban — place with mass transit.

Rail transit, especially, promotes density and that means more people living closer together, the defining characteristic of big city life. It's a life that's full of both sophisticated pleasures and deep frustrations.

But then you can say the same thing of the car-based lifestyle, which is where Honolulu will continue to head if the excise tax increase ends up dead and mass transit is stalled well into the foreseeable future. We'll be more spread out and more on our own, which in some ways continues to be the American dream.

You can argue the benefits of mass transit back and forth, and you can debate the value of raising taxes to pay for it. But this much seems certain: If the local funding mechanism ends up getting killed at this stage of the fight, it will stay dead for a long, long time to come.

"If we don't make transit happen now, it won't happen," Mayor Mufi Hannemann said recently. And he's right. Why?