As peak commute periods are the very reason mass transit solutions were first initiated, vehicles must have sufficient capacity and be capable of loading and unloading large numbers of riders quickly. In the densest cities this is best handled by longer trains and longer platforms. The longer trains and a need for unimpeded movement require a complete grade separation from other transit ways. All of this increased infrastructure is the basis for the 'heavy' rail label.
The Green Line Extension, the heretofore accepted plan for rail transit in Somerville/Medford, will make use of a grade separated right-of-way, but otherwise implements a light rail mode of transit. The intended market is as dense as that which the Red Line serves, though its stations will not be as conveniently located. If this rail expansion into Somerville were done correctly the ridership could approach that of the Red Line, which would mean roughly 88,000 weekday trips.
The MBTA has estimated 52,000 trips, per weekday, for the Green Line extension, but that is a misleading statistic, because it is not exclusive to the extension. Included in the stat are riders entering or departing from the existing Lechmere Station, whose portion of the total is by far the largest of any station on the extension.
But we can use that figure for looking at the demand for outbound trips towards Somerville from the central business district in the afternoon rush period. Estimating that the 2-hour PM peak period will experience 25% (13,000) of those daily trips in the outbound direction means moving 6,500 passengers/hr along the new line, from Boylston, Park Street, Government Center, Haymarket Square, North Station and Community College Stations. And these are added to the numbers who already move between these stations to transfer to other lines.
The GLX plan is for 'D' and 'E' branch trains to operate to Lechmere Station, with 'E' trains then servicing the Union Square branch and 'D' trains the West Medford branch. Together the two services can provide 6060/hour during peak time, but beyond the first station of Lechmere the capacity per hour will be 3030 (using 3-car trains). The MBTA could send both the 'B' and 'C' trains during peak hours to operate on the extension, increasing capacity. The 'B' branch can use 3-car trains, but the 'C' branch is limited to 2-car trains, thus the maximum capacity addition would be 5050/hr. If both the 'B' and 'C' are run to College Ave., that branch would then have a peak time capacity of 8080/hr.
The trunk of the Green Line, that section where all branches provide service, during peak hours is already operating at a 90 second headway, which is likely the minimum headway that can be achieved on the line without reducing speeds. Thus, the effective maximum capacity for the extension out to College Ave. is 8080/hr. If Union Square is not at capacity, the 'E' branch service to it could be traded out with the 2-car trains of the 'C' branch, letting the 3-car trains of the 'E' branch run out to College Ave., which would add another 1010/hr to the service.
The planned service on the Green Line extension appears to already fall short of what is needed to handle peak period demand, given the ridership estimates. If the estimates are low, or if the demand grows much it is clear that the Green Line's limitations will create headaches for both riders and the MBTA.
Already, cries from users of the Park Street Station are so loud that the MBTA is being pushed into another major financial expenditure to connect the Blue Line to the Red Line at the Charles/MGH Station, in order to relieve congestion at Park Street.
[ That expensive band-aid, if implemented, would be yet another ill-thought and costly stumble in MBTA planning. There is no far reaching benefit in connecting the Red and Blue lines at MGH. Instead, the Blue Line should be veered westward from State Station to run beneath the Red Line at Park Street, achieving the Red-Blue connection and thus reducing the Green Line platform congestion while also making viable an extension of the Blue Line into the heavy demand area of Back Bay and beyond. It makes little sense to dead-end the Blue Line at MGH. ]
Is adding 30,000 commuters to the congested Green Line stations in the central business district the MBTA's best solution? The estimate of a net increase of 30k weekday trips, on top of the current 236k, will bring the Green Line to 266k daily weekday trips, that is 44% more than the Orange Line's weekday trips.
This is a scenario which will weaken the appeal of this new line, causing it to fall well short of its potential ridership, and vastly reduce its cost effectiveness. Complaints will become standard, and cries for something to be done routine, but nothing will ever be done, because "it's too late to change it now," comes the reply.
So far, the planners in Boston are passing up their best opportunity to meet the needs of riders in Somerville and Medford. Other cities would be salivating over such a gift rail corridor, where added transit benefits can be achieved without heavy outlays.
The MBTA maps don't distinguish between light rail and heavy rail, but the MBTA knows, or should know, the realities of what each can provide, and the role which the Green Line should play in Boston's collage of transit options.
Given that a linear and unimpeded right of way, stretching up to five miles from the Boston CBD, is available and that the market to be served includes a densely populated area, perhaps there is a better solution.
A Track Not Yet Taken
The tracks of the Somerville/Medford rail corridor (current Lowell Commuter Line) run to within 200 feet of the MBTA's Orange Line tracks just north of the Community College Station. The only thing lying between these two lines are the set of tracks running out of North Station to Malden and beyond. The removal of a few abandoned/unused freight sidings which the Lowell Line tracks currently bridge over would allow grading the Lowell Line tracks down to pass under the northbound commuter tracks and then merge with the Orange Line tracks which are at surface level beneath the I-93 viaduct.
The actual connection between the current Lowell Line track and the Orange Line could take as little as 1000 ft. of realigned track, without a need for new rails. A very short new connector from the Malden tracks to the BET facility tracks would be laid to replace the one currently running underneath the Lowell Line astride the freight sidings. The change of grade for the new branch of the Orange Line to run beneath and then resurface to meet the Orange can be accomplished in a relatively short distance, unlike typical railway grade changes.
In the photo below, the dashed blue line is the current link from the Malden tracks to the BET tracks, and the solid blue line indicates the replacement for that connection. The bridge which the Lowell Line tracks traverse over the BET link and the freight sidings would be removed (and if in good condition could be used in helping to double track the commuter lines through Malden). The tracks could then be graded down from a point before the bridge such that they will easily pass under the Malden tracks.
From the point of the outbound track having cleared the main Orange Line tracks, as shown on the map, it is 1/4 mile from the next station, ample distance to resurface and merge into the main line.
If that estimated 30,000 trips were added to the Orange Line, it would still have less ridership than the heavily used Green Line.
As proposed in the GLRevisited, the Orange Line would provide speedy CBD access to residents of Somerville and West Medford. It will extend service 1.2 miles farther out than the current GLX proposal, giving service across the Mystic River into West Medford. It would actually have fewer stations than the total GLX proposal, as it would not service Lechmere or Union Square; Lechmere would remain as is, a Green Line station and not relocated as the GLX proposes.
As the price estimates for the GLX already include stations with gated fare control and other features of typical heavy rail stations, platform length would be the chief differential between an Orange Line station and a Green Line station. Thus we have 2 less 'heavy' rail stations to construct, while adding platform length to the other five stations.
The Green Line Revisited wants to promote an extension of the Green Line, but not have it be confused with the current GLX proposal which uses light rail vehicles with a heavy rail implementation. The GLR looks to extend the Green Line with a TRUE LIGHT RAIL implementation, which also means a true lighter cost. Be sure to read these two pages: 'The Name Game' and 'The Green Line: "I Am What I Am"'.