There’s a remarkable graph that has starred in blog posts and news stories with some regularity over the past year. It shows vehicle miles traveled in America over the last quarter century or so. For most of the period, the line rockets upward, straight and true, preparing to blast off the page. But then the strangest thing happens. In 2004, it starts to level off. And in 2008, it begins to decline.

The tale behind that line grows in significance by the day. That rocket-ride upward corresponds fairly directly to the economic story that has culminated in the current crisis. Americans moved outward from cities in droves in the 1980s and 1990s, buoyed by cheap oil prices. Commute times soared as metropolitan areas stretched into the distant exurbs, many of which now lay devastated by housing defaults and foreclosures. As demand for oil increased, so too did prices, which led to a stream of money flowing into the Persian Gulf. Gulf nations recycled it back to us by buying American debt, thereby facilitating the massive borrowing that fueled the housing bubble.

In the end, high oil prices also helped to pop that bubble. The squeeze expensive gas placed on household budgets helped push marginal homeowners over the edge, fueling the credit conflagration, before finally exhausting the American consumer and tipping us into recession. And an epic recession it will be — large enough to sink oil prices and the international financial system that sustained American debt-supported consumption.

The line also embodies a significant change in the mindset of the American commuter. As vehicle miles traveled have fallen, transit ridership has exploded. We learned this week that rider numbers in the third quarter were 6.5 percent above their level a year ago (which was itself a record-setting year). Even as gasoline prices have crashed amid global recession, the gains have proven durable — preliminary October figures show steady, high transit use. For a nation that moved relentlessly away from center cities and transit for a half a century, and spent trillions of dollars making it nearly impossible to get around without an automobile, the turning of the tide is momentous.

So, too, is the political shift. Just last week, the Federal Transit Administration approved the construction of the Silver Line, a new Northern Virginia addition to Washington’s Metrorail system — and one that the FTA nearly killed a year ago. Describing the decision, Rep. James Moran (D-Va.) said, “[T]he ideologues in the administration have given up.” And no wonder, after the electoral drubbing Republicans received in November.

Now President-elect Barack Obama, seeking to lift the economy from its doldrums, is promising the largest public-works spending push since Dwight Eisenhower’s interstate highway system. Nervous greens have focused on Obama’s promise to repair the nation’s crumbling roads and bridges, but this is misguided. The incoming administration has asked local governments to deliver a list of ready-to-go transit projects for inclusion in the stimulus package, which has already turned up an estimated $12 billion in items that can be kicked off within 90 days, with a further $20 billion available inside of two years. And the Center for American Progress, not quite the official policy house of the Obama administration but close (its head, John Podesta, is running the Obama transition) has released its proposed stimulus package, which includes road spending equal to half the average annual amount allotted to highways and transit spending twice the annual amount normally bestowed.

We are beset by political, economic, and social realities that were outside the realm of the possible just a few years ago. For decades, we thought that building one way was the route to prosperity. We were wrong, as it turns out — dramatically so. Remarkably, we seem to have learned our lesson. No longer can our geography and our economy be described by a single, unsustainable, upward-sloping line.