Daily Misery Has a Number: Commute 2nd-Longest in U.S.

"Those commuter buses fill up as soon as you put them on," said Ronald F. Kirby, transportation planning director for the Metropolitan Washington Council of Governments. "Particularly where you have HOV facilities, it's an attractive option."

Kirby said the apparent drop in carpool use between the 2000 Census and the 2005 survey matches local research showing the same thing.

"A good part of that is a mirror image of transit increasing," he said. "Every time we increase transit, we soak up carpooling. It's the same market. They are the kind of people who are trying to avoid driving alone. Carpooling is somewhat of an inconvenience. If transit service improves or someone gives you a subsidy -- forget the carpool, I'm going to transit."

But transit use is also rising in closer-in jurisdictions. Metrorail trips grew 17 percent from 2000 to 2005. The system has opened several stops since 2000.

But Dan Tangherlini, Metro's acting general manager, said: "We have seen large increases in the core stations as well. Some of our biggest-growing stations are places like Gallery Place, which has grown as a destination in and of itself."

Tangherlini said that when the system updates its survey of rail riders this year, "I've got some friendly bets here we will see large increases in out-of-compact origins" -- people who drive in from exurban counties that do not have Metro stations.

The American Community Survey is a detailed national survey of households that is the planned replacement for the long form in the 2010 Census. The survey does not yet cover the entire population -- it leaves out the small percentage of people in college dormitories, prisons, nursing homes and other "group quarters."

Database editor Dan Keating contributed to this report.