In Maryland, the Purple Line will be a heavy influence on which candidate D.C. suburban voters cast their ballot for in the governor's race.
Republican former Gov. Bob Ehrlich wants the Purple Line to be rapid buses, saying it is cheaper and more likely to receive federal funding. Incumbent Democrat Gov. Martin O'Malley wants light rail, saying, among other reasons, it is more attractive to potential businesses looking to locate in the D.C. suburbs.
That stance helped O'Malley receive the endorsement of the Greater Washington Board of Trade.
"We're at capacity on certain lines already on Metrorail. When you look at buses, they fill up pretty quickly, they don't move as many people, and they don't move them as fast," says Jim Dinegar, the board's president.
A Maryland Transit Administration study also termed light rail better for the environment. But the World Resources Institute in D.C. did its own study, which says rapid buses are better. The institute's Greg Fuhs says they produce fewer greenhouse gas emissions.
"The primary reason being the energy source for light rail, the region covered by the Purple Line system, is heavily coal dependent," Fuhs says.
Fuhs adds many buses now run on cleaner fuels than gas and get better gas mileage.