O'ahu's record-busting traffic breakdown may go down in the annals as Black Tuesday. That color certainly describes the mood of thousands who finally crawled home in the wee hours yesterday.

We all know alternative routes are limited because of our island topography. Even so, who could believe Tuesday's traffic mess would be so bad?

Believe it: O'ahu commuters shuttle between work and home along a narrow artery with few collateral branches. There's little margin for error, and if an error happens to shear concrete from a pedestrian overpass and compel its removal during rush hour, the arterial blockage is severe.

The worse-case scenario became reality. Transit officials made the speedy and correct decision to remove the unsafe structure, working through the night so that the morning commute could resume with something approaching normalcy.

There were no palatable alternatives, and that is a knotty and frightening problem. If a major catastrophe were to force a massive evacuation, it's chilling to think about how helpless we might be.

This does not mandate a rush to embark on a new highway building scheme. There's little room on our small island for another massive east-west corridor, and double-decking the existing highways might not warrant the expense or the aesthetic blight except in rare circumstances.

A contingency plan, one that presses for improvements to detour routes and coordination with bus service, would be a wise move. And this plan should envision strategies that involve alternative conduits.

If the city follows prevailing instincts to develop a fixed-rail transit system, for example, it should be one that would not be derailed by freeway troubles, even if it does follow the same general alignment.

A ferry route sounds like a rational option as well.

But before the island buries itself in blueprints, Tuesday's events show how much we need to enforce the rules we already have. While military and civilian authorities continue investigating the circumstances of the accident, it's certainly clear that rules for transporting oversized equipment need to be strictly enforced. And, looking ahead to a time when military uses of our roads are bound to increase, the hours for transporting such vehicles on public roads should be limited.

Keeping a small, populous island like O'ahu functioning well is, above all, a question of balance.