(Washington, DC — David Schultz, WAMU) Some cities use letters or numbers to name their train lines; here in D.C., we use colors. Depending on where you're going, you take the Red Line, Blue Line, Green Line, Orange Line or Yellow Line. The iconic D.C. Metro map is an artful study in the use of these five primary colors.

But for years, there's been talk of a new color - the Purple Line. Until recently, the Purple Line has been more myth than reality - in part due to the light rail project's nearly $1.7 billion price tag. In the past four years, however, Maryland Governor Martin O'Malley (D) made it a priority and has begun seeking federal funds for the Purple Line.

O'Malley is up for election this year and Bob Ehrlich, his Republican opponent and his predecessor as Governor, is not a Purple Line supporter. And that may end up costing him the election.

Ehrlich says he prefers the Purple Line to be a bus rapid transit system rather than a light rail line, which he says would cost about a third as much.

This stance that has endeared him to conservatives in Maryland who think O'Malley has spent taxpayer dollars freely and unwisely. Problem is, it's had the opposite effect in vote-rich Montgomery and Prince George's County - the would-be locations of the Purple Line.

It's worth noting that, unlike with the region's other multicolored train lines, no part of the Purple Line would travel into D.C. proper. Instead, it would connect Montgomery and Prince George's, two of D.C.'s affluent Maryland suburbs and both areas with crippling traffic congestion. That these two suburban counties could warrant their very own light rail line is a sign of just how populous and economically prosperous they have become. From a strictly demographic standpoint (32 percent of all Marylanders live in Montgomery and Prince George's), it's hard to see how anyone can become Maryland's governor without their support.

The D.C. suburbs are heavily Democratic, so perhaps Ehrlich never had a shot there anyway - Purple Line or no Purple Line. Or perhaps he figured, in The Year Of The Tea Party, coming out against the project would win him more votes than it would cost him.

Either way, Ehrlich appears to be in trouble. A gap in the polls between him and O'Malley has been steadily widening since this summer, and some local observers are wondering whether he can win without at least a respectable showing in the D.C. suburbs.

Of course, this race is about much more than support for or opposition to a light rail line. But, if Ehrlich does in fact get trounced in Montgomery and Prince George's, his stance on transportation issues will have played no small role.