The City of Sacramento took a giant leap on Tuesday when the City Council approved Thomas Enterprises' plan to redevelop the rail yards just north of downtown. But there is no guarantee the direction that Sacramento leaped is forward.

On the other hand, the project might be exactly what Sacramento needs to ditch its cow town image. For years, city officials have longed for redevelopment of the Union Pacific rail yards — the western terminus of the transcontinental railroad. And why not? Wedged between downtown and the American and Sacramento rivers, the site is potentially one of the great urban infill locations in the United States.

With any such opportunity, progress is slow. Union Pacific has not always been a willing partner. Nearly four years ago, our Morris Newman wrote about a different developer's run at the site. In 2006, voters reject an ill-defined, sales-tax-funded basketball arena project on the site. In the meantime, the housing market shot to the sky and then fell to earth.

So give the city and Georgia-based Thomas credit for plugging away.

There is no doubt the plan is ambitious. It calls for up to 12,000 residential units, more than 1 million square feet of retail space, multiple office towers and hotels, a cultural district surrounding new railroad museums, waterfront development on the Sacramento River, and a multi-modal transit center. The vision is of urbanity.

But there are reasons for concern:

• At 240 acres, the site is enormous. Great cities typically are built one block at a time, not with sweeping strokes by a master developer.

• The up-front infrastructure costs are equally enormous (at least $740 million) and funding is uncertain. The plan counts on $150 million from the state's 2006 housing bond, which appears overly optimistic.

• Early phases of development will be heavily oriented toward retail. Thomas and the city like this approach because retail generates money for further development and for municipal coffers. However, the plan requires Thomas to develop only 1,000 housing units within the first 10 years. Without residents, the rail yard project is just another "lifestyle center," which is Thomas's specialty.

• It appears the first thing to get built will be a Bass Pro Shops, a 200,000-square-foot big-box with a giant parking lot. So much for urbanity.

• What about the existing downtown? Sacramento's downtown is OK, but it's not thriving. Redevelopment has faltered for decades, as evidenced by the endless struggle to remake the K Street mall. If capital starts flowing to the rail yards, who's going to be left to invest in downtown? Heck, who's going to be left to live, shop and eat in downtown when there's a spiffy new district just next door? Westfield, which owns the Downtown Plaza shopping mall, opposes the rail yard project for just this reason.

• Which brings me back to size. Downtown and midtown Sacramento have long suffered from a lack of density. There simply are not enough people and stuff crammed together to create the sort of urban vitality found in San Francisco, Portland or that other big government town, Washington, D.C. An additional 240 acres of development may simply dilute things further.

Still, there are also reasons for hope. As I said, this is potentially one of the great infill sites in the country, and infill is something that cities in the Central Valley need much more of. Sacramento is trying to think big and long-term, and, again, that approach is needed in the Central Valley.

Not long ago, Sacramento would have been willing to convert the rail yards into a basketball arena with 8,000 parking spaces, a couple big-box power centers and a two-story office park. In other words, it could have become North Natomas without the housing. Instead, there's an opportunity to make a real city.

- Paul Shigley