Light rail isn’t just tracks and trains full of commuters. It’s also a way to build better cities, channel growth and slow sprawl.

The South Sound needs it as a reliable alternative to Interstate 5 and to spur intelligent urban development in the corridor between Sea-Tac Airport and Tacoma.

A good example of intelligent development can be found in Seattle’s Rainier Valley. The light rail line through Seattle is still a year away from opening, but it has already begun to transform the communities it will run through.

The Seattle Times reported last week that private developers are proposing to build more than 1,500 condominiums or apartments within a short walk of what will become Sound Transit rail stations in the Rainier Valley. Seattle officials say they’ll be the first multifamily projects built there without public subsidies in more than three decades.

Martin Luther King Jr. Way, the valley’s main drag, is now dominated by old strip malls, parking lots and the like. It’s the corridor the car built, and it takes a lot of driving around to run errands, shop or get anything done. The new, rail-oriented development promises a denser population with stores and other amenities – not to mention the train station – within walking distance.

The Puget Sound region as a whole will never look like this. There will always be suburbs and single-family homes – that’s an option many people will always want to have.

But the dense, transit-intensive option is also crucial. It draws people inward to urban services, easy commutes and rich entertainment and retail offerings.

The creation of multi-story apartments and condominiums near the stations in the Rainier Valley demonstrates the magnetism of light rail. The extension of rail transit from Sea-Tac to Tacoma would have the same effect on development in that corridor. As the region’s population grows, the result would be much greater housing density along Highway 99, where the line would mostly run.

This makes infinitely more sense than pushing newcomers out to new developments around small towns and in rural areas – a pattern that has overwhelmed country roads with traffic and spread large numbers of people far beyond the logical reach of sewers, utilities, police and other urban services.

Light rail alone won’t halt sprawl, but it’s an important part of the solution. Regions with large populations don’t work unless most people live in cities – the denser the better. Rail transit makes that an attractive choice.