Here is a breakdown of each line, the number of grade crossings, the distance of the first grade crossing from the terminal station (i.e. how many miles is the line grade separated before the first crossing) and the total length of the line. Also noted are any major stretches which are already grade separated. Distances taken/estimated from the MBTA’s Blue Book (pdf). Here’s a map and list:

The crossings on the Worcester Line, while bothersome, are not the major reason for slowdowns on that stretch (even the fastest trains run the length of the line in 1:20, an average speed of only 33 mph). All trains stop at Framingham (where the two most congest crossings lie) and Ashland is only a few miles past. If there were plans to dramatically upgrade this line to higher speed operation, say, to provide 50 minute service times from Worcester, then the crossings would be more troublesome. For now, once the state completes the purchase of the line, they’ll need to work to upgrade speeds and dispatching before they tackle bridges. Additionally, Framingham may be rebuilt to deal with traffic congestion, and such a project wouldn’t be cheap since there are several intersecting freight lines which would need to be separated, too.

The Franklin Line’s crossings both border stations, and the Franklin Line does not serve a large anchor city at the end of the line (an extension would be possible to Milford, but Milford is only a quarter the size of Lowell). Since the grade separations are near the end of the line, it would only benefit a few of the passengers to make costly changes. 

The Lowell Line, however, has ridership as high as the Franklin Line (in a shorter distance) and also hosts some trains from the Haverhill Line as well as Amtrak’s Downeaster trains from Portland. The Worcester Line’s ridership is higher, but much more spread out. Half of the Worcester Line’s ridership lies east of Framingham, so a grade crossing there would add no benefit for them. Every rider on the Lowell Line would benefit from a West Medford grade separation. Additionally, with higher speeds, service currently serving Maine, and potentially serving New Hampshire, would be speedier. The Boston and Lowell—one of the first railroads in the country—was built in the 1830s to serve the mills in Lowell and has continued to be the main north-bound rail line throughout its history. Despite its age, it has low grades and wide turns and would be a good candidate for moderately-high speed train service (80-110 mph).

Then there are the operational efficiencies possible from eliminating the West Medford crossings. Most grade crossings have upkeep costs which include power and maintenance. In order to keep from having whistles blown, however, these High Street crossing has a paid attendant in little shacks 24 hours a day, one of two in the MBTA system (the other is at Greenwood on the Haverhill Line). This incurs an annual cost of $864,000 annually, or $432,000 for the Medford watchman. This still doesn’t keep motorists from breaching the crossing, which can tie up train service for hours and do quite a number of the car involved (if not, in this case, the motorist).

A grade separation would have obvious benefits: it would save half a million dollars per year in crossing costs, it would speed the trip for thousands of commuters on express trains through the station, it would remove a major safety hazard and it would ease traffic congestion where trains pass every ten minutes during peak hours.

How much would it cost? Hingham recently held up the state for $40 million in order to have a grade separation in their town. This included two approaches and 900 feet of tunnel; a similar length of tunnel (albeit a single track) than would be required in West Medford (this is assuming an 800-foot station in the cut and that the less-used Canal Street crossing was closed to allow for tracks to descend off the Mystic River bridge). The higher cost of burying two active-service tracks would be mitigated by the much broader footprint in the area. The right-of-way in West Medford is 60 feet wide and mostly borders roadways and industrial properties, the right-of-way in Hingham was only about 20 feet wide in places as it wound between commercial shops. One other factor may be the water table: West Medford is only about 24 feet above sea level (the level of the Mystic River is at sea level) so the bottom of the cut would be near sea level, and possibly impacting the water table. With that said, the Hingham tunnel is similarly low.

And how would you do it? Well, I’d imagine a three-phased scenario. First, slurry walls would be built on either side of the current tracks to act as the supports for the final trench, as well as any utility work at the current crossings. The current tracks would then be replaced by shoo-fly tracks on either side and the trench excavated, and a bridge built at the High Street crossing with the road rerouted temporarily there. Finally, the tracks would be relaid through the trench and the station rebuilt akin to the Waverley Station in Belmont.

Why not an elevated station like in Winchester? In Winchester, the 1950s-era grade separation replaced half a dozen crossings, not just one or two. (HistoricAerials.com from 1955 shows the route during construction; it also shows Waverley just after it was completed.) It also created a wall across the community (albeit a wall safer than the numerous grade crossings on the busy main line). That being said, it would likely be struck down by locals today, especially by many nearby residents in Medford (which has many houses near the tracks).

The main issue would be lowering the tracks quickly enough to provide clearance. It is about 1000 feet from the end of the Mystic Bridge to High Street. Assuming the river bridge isn’t rebuilt (although it might be a good time to do so) a 2% grade would lower the tracks 20 feet by High Street, more than enough for clearance. A slight deviation in the street, raising it three or five feet, would dramatically reduce the grade. Electrification of this route would solve any grade issues.

Once separated, this track, which is relatively straight from Boston to Wilmington and beyond, could be upgraded to speeds of 79, 90 or even 110 miles per hour. This would shave minutes off of travel times to Lowell and Portland, and potentially Nashua, Manchester, Concord and beyond. With Interstate 93 gridlocked for hours each day, rail service to New Hampshire and Maine makes sense, and grade separating West Medford can make this service more time-competitive while making West Medford quieter, less congested and safer.