As the price of oil rises and concerns about global climate change intensify, it's good and important that we're talking about developing more efficient vehicles, such as hybrid cars, and lower-carbon fuels, such as biodiesel fuel.

However, a new report by the Urban Land Institute (ULI) says we're missing an important third component in that discussion: the amount of driving we do.

Here, some context is helpful: The U.S. is the largest emitter worldwide of greenhouse gases that cause global warming. Transportation accounts for one-third of carbon dioxide emissions in the U.S., and that share is increasing, growing from 31 percent in 1990 to 33 percent today.

In "Growing Cooler: The Evidence on Urban Development and Climate Change," ULI argues that technological improvements in vehicles and fuels are "likely to be offset by continuing, robust growth in vehicle miles traveled," or VMT, which in layman's terms refers to the amount of driving we do.

"Since 1980, the number of miles Americans drive has grown three times faster than the U.S. population, and almost twice as fast as vehicle registrations," according to ULI. "Average automobile commute times in metropolitan areas have risen steadily over the decades, and many Americans now spend more time commuting than they do vacationing."

The growth in driving stems from what planners call our "built environment," or, put in other terms, the way in which we've arranged our offices, stores, schools, roads and parks. That way has largely been sprawl which spreads everything out and requires long commutes to accomplish daily tasks.

Because of this land-use pattern, the amount of driving we do is projected to increase and off-set gains won through new fuel efficiencies and alternative fuels, according to ULI. It's worth quoting ULI's report at length:

"The U.S. Department of Energy's Energy Information Administration forecasts a 48 percent increase in driving between 2005 and 2030, outpacing the projected 23 percent increase in population. The rapid increase in driving would overwhelm both the increase in vehicle fuel economy and the lower carbon fuel content required by the Energy Independence and Security Act of 2007.

"Carbon dioxide emissions from cars and light trucks would remain at 2005 levels, or 26 percent above 1990 levels in 2030. For climate stabilization, the United States must bring the CO2 level to approximately 33 percent below 1990 levels by 2030 to be on a path to a CO2 reduction of 60 to 80 percent by 2050."

So, what do we do? What third initiative, along with hybrid vehicles and alternative fuels, should we pursue? ULI says the answer is more compact development which helps people live within walking or bicycling distance of some destinations they need to reach everyday, such as work, shops, schools and parks, as well as transit stops. If people hop in their cars, then their trips are short.

Compact development is also known as "infill development" or "redevelopment" or "transit-oriented development." And it's doing the job of reducing the amount of driving that occurs in cities that have embraced compact development, including Portland, Ore., and Boston. Conversely, in sprawling Atlanta and Raleigh residents "racked up more than 30 miles driving each day for every person living in the region," ULI says. "In more compact Boston and Portland, residents drove less than 24 miles per person per day."

The ULI study is more good news than bad for the Puget Sound region. It's good news because data show our region is moving toward more compact development. Meanwhile, business leaders in the region are forming new alternative-energy companies and trying to lasso additional capital to create "green" jobs and alternative ways to power our economy.

However, the region's weakness is a lack of robust transit service connecting its population hubs in King, Snohomish and Pierce counties. Yes, transit service within those counties is good, but regional transit service connecting our urban archipelago is not as good as it could be. We need more commuter trains that run more often. We need light rail that makes sense, serving well-populated corridors, and that can be built within a reasonable time.

Sound Transit is debating how to ask voters to raise their taxes to pay for more transit service. If the agency goes to voters in November, one wonders whether the ULI study linking driving, land-use and global warming will factor into the discussion.

And that's really the point of the ULI study: Compact development is good, but compact development linked to robust transit service is far, far better. If vehicle fuel economy and alternative fuels are two legs of the three-legged stool that is transportation CO2 reduction, ULI says, then the third leg is reducing the amount of driving we do. And "a stool cannot stand on only two legs."