A few lines have been graced with two hour, clockface headways (Worcester, Lowell, Franklin)—not frequent, but at least predictable—but most others have service only every three hours, and sometimes less frequently. Combine that with variable headways and a lack of off-peak fares, and it's not surprising that ridership is less-than-stellar.
I suggested adding a station at Walden Pond, and today I'm going to go a step further. Rework the schedules, adding a small amount of service, to provide two-hour, clockface scheduling on all North Side lines. (I'll leave the South Side to someone else, for now, although boy could the Providence Line use better service!) A caveat: I'm not sure about how crew rules work, and that may be the cause of some of the schedule irregularities here, but we should design a schedule for passengers first, and crews can be shuffled between lines at layovers to shorten or lengthen shifts as necessary.
Newburport/Rockport is relatively easy. The current schedule works relatively well, but has some bizarre gaps. For instance, Rockport has inbound trains at 7, 10, noon and 2, and then a 3:10 gap before the next train. Going in to Boston for the afternoon? You can arrive at 3 or 6. At the beach and want to get back to the city? You can go home at 2 or 5, but not in between. Even at Salem, where the two branches interline, there is a nearly two-and-a-half hour gap between 3:20 and 5:46. For a city with a significant tourist draw (the witch museum, the PEM), poor highway access and limited parking, this schedule is severely lacking.
The two branches of the line have run times of 64 minutes (Newburyport) and 71 minutes (Rockport), so it is relatively easy to interline the two with three train sets:
This does add some service, with one extra Rockport trip and two extra Newburyport trips each day, adding about 22% to the current service. But the utility increases dramatically, with predictable train schedules and the elimination of service gaps. In terms of service hours, this schedule adds 6:38 to the schedule. The marginal operational cost per service hour, as calculated pertaining to the CapeFlyer, yields an extra cost of about $4500 per day. The line currently carries 5600 passengers on the average weekend day. Assuming an average fare of $7.50, just 600 additional riders—an increase of 11%—would cover the operational costs of these additional trains.
Fitchburg and Haverhill, however, are harder. Haverhill has a run time of 65 minutes, long enough that a single train set shuttling back and forth (see Lowell) can't make a round trip in two hours, so the current schedule has service every three hours (or so), which is hardly useful. The Fitchburg Line's current schedule is awful, with three-hour-plus service gaps and then short-turns running within a half hour of other trains. The line is long enough that even with the new schedule accounting for higher speeds, the line would not even be able to attain two hour headways with two sets. The schedule is better than the current one, it's nowhere near clockface, with service about every 2:25, or so.
But there's no rule that says a train on the Fitchburg Line has to run the Fitchburg Line all day and all night, right? Imagine Fitchburg and Haverhill as two branches of the same line, with a train running first to Fitchburg and then to Haverhill, kind of like the Rockport and Newburyport lines. The relatively short Haverhill Line interlines well with the long Fitchburg Line, and the same three train sets can, combined, provide service every two hours on both lines.
I think that's pretty elegant. This requires just 4:12 more running time each day, or $3150 of marginal operational costs. The two lines have a combined ridership of 4500, and would require just 420 additional riders—a 10% increase—for fares to cover the costs. And the benefit would be high: the frequency of trains on the Haverhill Line would increase by 50%, from every three hours to every two.
One final idea would be to have the trains operate on a "pulse" system at North Station to enable transfers, which is attainable if every line has clockface scheduling with the same headway. Every train would arrive at a similar time, allowing passengers going from, say, Lynn to Waltham, with an easy transfer at North Station (assuming trains are on time). With the current schedules, this isn't possible. With a couple adjustments, the above schedules, with the Lowell Line, would work quite well for that.