There is no Light Rail Proposesd between DC and Baltimore, they have a Commuter Rail that already connects both cities. The three freeways that connect DC and Baltimore are no where near causing sprawl like most of the Highway's in Northern Virginia.
What is soo smart about Smart Growth in Maryland when most of the old buildings that are renovated contains Lead posion and molds. Your land use adjustments statement is just another way of saying that the Maryland suburbs is not worthy of Developing at the same high rate as Virginia which seems EXTREMLY biased especially if no one is suggesting that Northern Virginia should have land use adjustments and rehabilitating older buildings so there would not be soo much sprawl spreading to the western and southern parts of Virginia.
The ONLY way they will take down the freeways in Maryland like you suggested and replace them with light rails WILL be the day that Virginia and other states take down ALL of their Freeways and replace them with Commuter rails. Until that happens(when pigs fly) Maryland will continue to build new Highways along with Commuter Mass Transportation just like Virginia.