Robert O.C. Worcester remembers a time when he rarely saw a Pennsylvania license plate on Interstate 83 near his Baltimore County home.

 And if he did, "you could just assume it was someone driving through," said Worcester, a Baltimore native.

 No more.

 Worcester, president of Maryland Business for Responsive Government, said "it's at least 50/50 now" between Pennsylvania and Maryland license plates on I-83 at rush hour. He added that, while rush hour used to be a breeze, now "you can expect to go around three to five miles per hour" at some spots.

 More than 157,000 people left Maryland for other parts of the country in 2006, while just 137,000 moved in, according to data from the Internal Revenue Service. That 20,000-person net loss capped a three-year run that saw a loss of 35,000 Maryland residents.

 Economists believe the chase for jobs sparked many of those defections, especially to the fast-growing South and West.

 But Mark Goldstein, an economist for the Maryland Department of Planning, also said it was likely that many Marylanders are keeping jobs here and migrating across state lines to take advantage of cheaper real estate prices in Pennsylvania and West Virginia.

 Goldstein said he did not have data to prove that hypothesis, but real estate agents in neighboring states say Marylanders are crossing the border in their housing search.

 Jerry Pilgrim, a real estate agent just across the Maryland border in York County, Pa., estimates that 80 percent of his clients are Maryland residents, who can find a 4,000-square foot house in Pennsylvania for the cost of a town house in some Maryland counties.

 He said most of those leaving Maryland keep their jobs after moving north.

 "I've got people commuting all the way down to the D.C. area, some as far as Reston," Va., Pilgrim said.

 Pilgrim said sales to Marylanders have slowed recently, but not because of problems in Pennsylvania.

"We're having to deal with renters because owners are not able to sell their houses," Pilgrim said.

 Shanna Wiest, governmental affairs director for the Realtors Association of York and Adams Counties in Pennsylvania, said more Baltimore County residents migrated to York County in 2005 than anywhere else in the country, including neighboring counties in  Pennsylvania.

 Four other Maryland municipalities -- Baltimore City and Anne Arundel, Carroll and Harford counties -- placed in the top nine.

  Sean Dobson, executive director of Progressive Maryland, cited Maryland's near-full economy and its status as the wealthiest state in the nation as evidence that migration from the state has been caused by not enough "money trickling down" to lower-wage workers.

 Dobson, whose group backed the living-wage bill that became law Oct. 1 and continues to advocate for more progressive tax codes, believes state lawmakers need to do more to improve wages and make housing more affordable in the state.

 But Worcester disagrees, saying Maryland residents are already overtaxed and that adding more taxes would not stem the tide of migration.

 Allowing taxpayers to keep more money in their pockets also would bring in more tax revenue for the state, Worcester said. But state lawmakers "just don't understand that less taxes equals more revenue."