I have argued to keep the Yellow Line a valid and current piece of Baltimore's Regional Rail Plan for what seems like an eternity. I have also to a lesser extent been on board for the creation of the Charles St. Trolley. So which do I want? There are those who think it's either one or the other and because of cost, the Charles St. Trolley would always win. Why should it? I mean why should the two compete? Can't the two exist together? I think so. 
With the existing Central Light Rail Line, Downtown, with both new lines built will have three north-south lines serving it. Now I consider the Downtown boundaries to MLK Boulevard to the west and President St. to the east, pretty much every north south thoroughfare is congested. Now each of the three lines will ultimately end in different places and will vary in length. 
The Charles St. Trolley and the Yellow Line, at least for a short period of time will be side by side. The Yellow Line will go underneath both Charles St. and Light St. at the Charles Center Green Line Station where space was made available for a transfer line when it was built. I consider the smartest pre-planning in modern Baltimore Transit History.
Now does the current Light Rail go, and where will the Charles St Trolley and Yellow Line go? Well, the Light Rail goes from Cromwell Station in Glen Burnie to Hunt Valley. Past Downtown, it travels I-83 through the JFX Valley, Hampden/Woodberry, Mt. Washington, Timonium ending in Hunt Valley.
It has two branches one for BWI Marshall Airport, and another for Penn Station. The creation of the Yellow Line will make these a part of that line making the Central Light Rail Line a straight shot from Cromwell Station to Hunt Valley. Short term southern expansions would include the redeveloping "Glen Burnie Town Centre" on Crain Highway. Long Term would include traveling down I-97/Ritchie Highway with stops at Marley Station (Pasadena), Greater Baltimore Washington Medical Center, Servena Park, and finally ending in Annapolis.
The Yellow Line will expand southbound from the Light Rail Line's BWI Marshall Airport Branch for stops at the BWI MARC Station, Baltimore Commons, Arundel Mills, Dorsey MARC, Snowden River Parkway and Route 108, East Columbia, and finally ending at Columbia Town Center (West Columbia pictured abobe) where it will eventually meet the DC Metro's Green Line.
On the other end from Camden Yards, it will go northeast along Conway St. for an Inner Harbor Stop, then to the Charles Center Green Line Station for two, a stop for Mercy Hospital, City Hall, and the Court House. It will continue along Calvert St. for a Mount Vernon Stop traveling north to be replace the Light Rail's Penn Station Stop that will also serve the up & coming Station North Community. 
I should also point out that the Yellow Line will be needed if the JFX were torn down to relieve the additional traffic congestion. The two projects should be funded as one. 
Back to the Yellow Line, since splitting from the Light Rail Line at Camden Yards, it has mirrored the proposed Charles St. Trolley Route, well that ends now. The Trolley, as its name suggests, will continue along the Charles St. Corridor. The Yellow Line, past North Avenue will serve the ailing Greenmount Avenue/York Road Neighborhoods. First stop 25th St. at the redevelopment hungry Neighborhoods of Barclay and East Baltimore Midway (pictured above).
Then, it's off to the old Memorial Stadium grounds where redevelopment has uplifted the area after the demolition of the Os former home. Waverly is perhaps the best area east of Greenmount Avenue.
Continuing up York Road we come to the Pen Lucy/Govans area. This area is improving one house rehab at a time. Hopefully the Yellow Line will inspire the redevelopment of the blighted Old York Road which is holding the area back (pictured above).
Next we come to Belvedere Square, perhaps the best North Baltimore has to offer. Now we cross the County Line into Rodgers Forge. This well perserved Row House Suburb is bursting at the seams as long time Home Owners sell to young families. This has spawned the construction of West Towson Elementary School to relieve over crowding at Rodgers Forge. Next we come to College drive which will erve GBMC, Mount St. Joseph Medical Center, Shepard Pratt, and Towson University. Yep, this stop's a big one.
Finally the Yellow Line will end at Towson Town Centre where in its vicinity redevelopment has taken the area by storm.
Then, it's off to the old Memorial Stadium grounds where redevelopment has uplifted the area after the demolition of the Os former home. Waverly is perhaps the best area east of Greenmount Avenue.
Continuing up York Road we come to the Pen Lucy/Govans area. This area is improving one house rehab at a time. Hopefully the Yellow Line will inspire the redevelopment of the blighted Old York Road which is holding the area back (pictured above).
Next we come to Belvedere Square, perhaps the best North Baltimore has to offer. Now we cross the County Line into Rodgers Forge. This well perserved Row House Suburb is bursting at the seams as long time Home Owners sell to young families. This has spawned the construction of West Towson Elementary School to relieve over crowding at Rodgers Forge. Next we come to College drive which will erve GBMC, Mount St. Joseph Medical Center, Shepard Pratt, and Towson University. Yep, this stop's a big one.
Finally the Yellow Line will end at Towson Town Centre where in its vicinity redevelopment has taken the area by storm. 
Last we come to the Charles St. Trolley, unlike the two lines discussed earlier in the post, the Trolley will be very local and focused. I look at it as a means for College Students in the area (of which there are many) to get from School/Class to the clubs down by the Harbor without taking their cars. I know that's a narrow minded view of the Trolley but that's what comes to mind when I think of it. Although I find its purpose to be limiting, I do believe it will play a huge part in relieving traffic congestion. 
The Trolley will start at Charles and Conway and make its northbound through, Charles Center, Mt. Vernon, the Midtown Donut, Station North, and Charles Village. In the process it will run by the following Colleges, UMB, MICA Art Institute, UMB Mount Royal, and Johns Hopkins Homewood. Also major users of the Trolley could perhaps be workers at Univeristy of Maryland Medical Center and Union Memorial Hospital. The Trolley will have transfer points where there are stops for other rail lines. Its southbound track will be St. Paul St. 
Like I said, I have argued for keeping the Yellow Line in the general discussion as the Charles St. Trolley has been all but replacing it. For people who think I'm crazy for saying both when asked the question; "one or the other" I invite them to read this post and they will see the nececity of them both and the differing functions they will serve.
