When a co-worker asks if you take Metro to work and you say “yes,” are you leaving something out? For tens of thousands of Metrorail riders, the transit commute starts in a car.

Metro was built to be a car magnet. The rail stations were supposed to suck up car commuters in the suburbs and spit them out as rail riders in downtown Washington, where they would walk or take buses for the short trip to their offices.

That was a very green strategy for downtown, but not so much for the suburbs.

It spared the District and parts of Arlington County and Alexandria some of the agony that would have resulted from building more highways to funnel traffic into the dense core of the region. But in the decades since this hub-and-spoke rail system was planned, suburbanites have gotten the notion that they also could live in communities, rather than in random gatherings of bedrooms and parking garages.

Hence, plans to retrofit suburban centers such as Tysons Corner and Silver Spring. Across the region, we see townhouses and apartments rising from every available space near Metro stations.

Many of tomorrow’s suburbanites will work, live and play in the same area, if they can, or at least make it two out of three by living within walking distance of Metrorail.

But car magnetism is a powerful force, as I found out during my online discussion with readers on Monday. My response to one traveler’s point about the role of parking garages in creating congestion included this: “Metrorail also provides an enormous incentive to drive by surrounding its suburban stations with massive parking garages.”

The chat’s question-and-answer format is different from the one we usually follow in this column, in that chat commenters don’t include their names and home communities. Nonetheless, I think that sharing some responses to my statement will illustrate definitions of city and suburbs that need to change.

Q. “What? Metro’s garages give people an incentive to ride Metro into the city and keep their cars out. What do you think downtown traffic would be like without Metro’s garages? How are people supposed to get to the subway, unless you think Metro operates bus routes within walking distance of every home in the region? One of Metro’s biggest failings is that it didn’t build enough suburban garages. . . . Every car parked in a Metro garage is a car off K Street.”

Q. “If people’s lives were ‘home to Metro, Metro to work, work to Metro, Metro to home,’ sure other methods are great. However, who has that? Many people I know have errands to run after work.”

Q. “Would you rather have all of the cars on the Beltway or interior connectors? This is a very narrow-minded and short-sighted opinion.”

In response, let me first say that I’m against punishing commuters for following patterns they did not invent. But our four-decade history of surrounding suburban Metro stations with parking lots and garages encourages suburban sprawl and is unsustainable.

And what makes downtown sacred and the suburbs expendable when it comes to allocating extra traffic congestion?

Metro certainly cuts down on the number of car trips into the D.C. region’s core, which is swell for those who live and work in the core. But it adds tens of thousands of car trips each day in suburban communities. Many of those trips are short — just enough to jam streets and highway exits.

Fairfax County is the first suburban jurisdiction to adopt an anti-magnet strategy by declining to build more parking garages around the four Silver Line stations in Tysons Corner. I hope Fairfax leaders can resist the pressure to reverse that policy, so that Tysons can have a real shot at becoming a livable city.

But west of Tysons Corner, the Silver Line will follow a more traditional pattern. Wiehle Avenue, the end of the line for phase one of the project, has a garage big enough to warehouse 2,300 cars. In phase two, stations farther west will provide thousands more spaces for commuters — including some from West Virginia and western Maryland — who will drive many miles to become transit users.

This isn’t a call for everybody who works downtown to change jobs and trade in the car for a bike. Or a call for governments to raise Metro parking fees and put the financial squeeze on drivers. But just because we can’t do everything, doesn’t mean we should do nothing.

A greater investment in buses, bike lanes and walkable communities in the suburbs won’t end congestion around Metro stations, but it could ease commutes for everyone, including drivers.

Dr. Gridlock also appears Thursday in Local Living. Comments and questions are welcome and may be used in a column, along with the writer’s name and home community. Write Dr. Gridlock at The Washington Post, 1150 15th St. NW, Washington, D.C. 20071, or e-mail drgridlock@washpost.com .