Over the last year, several people at the Boston advocacy group TransitMatters have been working on a plan to restore night bus service in the area, which is one of few big US cities with no transit between 1 and 5 am. See here for the original concept, from March of last year. The TransitMatters plan assumes limited financial resources, designing the plan around eight or nine routes, all running on an hourly takt schedule, meeting at one central location for a pulse, currently planned to be Copley Square. This seems fairly standard: in Vancouver, too, the daytime bus grid is replaced with a pulse-based system at night, with 30-minute headways on most lines.
So far, so good. The problem is that after additional work, including checking travel times on Google Maps but also some nighttime test drives, TransitMatters found that the original map would not work with an hourly takt. Hourly service with one vehicle per route requires one-way travel time to be 30 minutes minus turnaround time. Double-length routes, at one hour minus turnaround times, can also fit into the system, with two vehicles, but nothing in Boston is that long. Several of the routes turn out to be just a hair too long, and the plan evolved into one with 75-minute headways, too long and irregular for customers. In meetings with stakeholders, the relevant members of Transit Matters were told as much, that 75 minutes was too low a frequency.
I started doing work on this plan around then. Since I think a clockface schedule is important – especially if there’s money for more buses, because then the headways would be 30 minutes and not an awkward 37.5 minutes – I started to sketch ideas for how to reduce travel time. The revisions center the schedule, fitting route choices around the need for buses to complete the roundtrip in an hour minus two turnaround times; this is what I came up with. Time is saved by avoiding detours, even to relatively major destinations, and by not going as far as would be ideal if there were no need to maintain the takt. Many of the design principles are generally useful for designing takt-based schedules, including for commuter rail and for rail-bus connections.
Schedule padding should be based on expected punctuality
This is a point I’ve made before in talking about LIRR scheduling, where fragile timetabling contributes to high schedule padding. Overall, punctuality depends on the following possible attributes of transit services:
- Rail is more punctual than buses, and electric service is more punctual than breakdown-prone diesels.
- Grade-separated transit is more punctual than surface transit.
- Services are more punctual when there are fewer riders, especially buses, which only stop when riders request it.
- Surface transit is more punctual if it has dedicated lanes, or if (as on some Vancouver routes) it runs on a street with signal priority over intersecting traffic.
- Surface transit is more punctual off-peak, especially at night, when there’s no congestion.
- Transit service is more punctual the shorter the span is: a system that’s only supposed to run for 5 night hours has less room for schedule slips than one that’s supposed to run for 21 daytime hours. (This I credit to Ant6n.)
While NightBus involves surface buses running in shared traffic lanes using on-board fare collection, the expected traffic is so low that travel time is likely to be close to the travel time depicted on Google Maps without traffic, and significant variations are unlikely. This means it’s possible to get away with less schedule padding, even though the plan requires 8 routes to converge at one pulse point. The maximum one-way travel time should be taken to be around 26 minutes. 24 minutes is better, and ideally not all routes should be 26 (they’d wait for one another at the pulse point, so it matters how many routes are near the maximum and not just what the maximum is).
Routes should run as fast as necessary and as far as possible
Sometimes, the optimal routing is already the fastest – for example, maybe it really is optimal to link two nodes with a nonstop route. Usually, it is not: on rapid transit there are intermediate stops, on surface transit there are detours and slower segments when freeways are available. When the schedule is tight, there is a plethora of tradeoffs that must be made about travel time. A detour to a major destination, so important that in isolation it would improve service despite the slowdown for through-passengers, must be weighed against other detours. On fast commuter rail line, where there is a significant stop penalty, the equivalent is the intermediate stop; I discussed this 5 years ago in the context of the Lowell Line. The overall length of the route is also a variable: when possible, the outer end should be as far as possible while maintaining the takt.
In the context of NightBus, I used this rule for all routes:
- The N17, running parallel to the Red Line to Ashmont, runs straight on Dorchester Avenue, whereas in the original plan it detoured to serve Kane Square; there is no time to detour to Kane Square, so in the revised plan it skips it, and passengers going there would need to walk 500 meters.
- The N28, running on Washington Street and Blue Hill Avenue, terminates at the future Blue Hill Avenue commuter rail stop, and not the Mattapan trolley stop. At night the trolleys don’t run, so the connection isn’t important, and the few hundred meters cut from the route give the buses 2 crucial minutes with which to make the 26-minute one-way schedule.
- The N32/39 cannot go on Huntington (N39) and thence to Hyde Park (N32); it can either go on Huntington to less valuable Roslindale or on a route parallel to the Orange Line to Hyde Park. I believe the latter option is better, but this is up for debate.
- The N57 follows the Green Line B Branch to Boston College (taking 20 minutes), not the 57 into Watertown (which would take about 27); I think this is also the optimal decision independently of the need to make the pulse, but the pulse makes it far better. Note that this means the route would have to use unmarked bus stops, since in the daytime there is no bus paralleling the B Branch.
- The N1 terminates at Davis Square, without going farther into Cambridge or into Arlington (as N77).
- The N82 and N110 use Storrow Drive to skip Downtown Boston’s slow streets. The buses run on a pulse, so there is no need for more than one bus to serve the same route – they’d be scheduled to bunch, rather than overlying to provide higher frequency. The N111 to East Boston, Chelsea, and Revere serves Downtown Boston instead. This cuts service from Downtown to Malden and Medford, but Downtown is a 9-5 neighborhood, so there’s less need to connect it in every direction at night.
- The N111 terminates in central Revere and not in North Revere.
Not all transit services are meant for all social classes
At night, buses go at approximately the same speed as cars, provided cars can’t take freeways. If the cars are carrying multiple passengers, as ride-sharing counterproposals plan to, then they probably can’t take freeways. In theory, this means buses would be for everyone, since they were as fast as taxis. In practice, this is only true for people using one route – diagonal trips are still faster by taxi. But worst, the hourly frequency is brutal. People who can plan their night travel around the schedule would use the bus; so would people who can’t afford taxis. But people in the top two-thirds of the income distribution are unlikely to use NightBus, or any ride-sharing alternative (if ride-sharing can afford more vehicles for higher frequency, so can buses).
What this means is that the service needs to be designed around the needs of low-income riders. As a note of caution, in popular parlance there’s a tendency to conflate low-income riders with other groups, such as elderly riders, and pit their needs against good transit practices like wider stop spacing, off-board fare collection, frequent grids, and so on. Those practices are applicable to everyone, and if they appear to favor middle-class riders, it’s because when the buses are too slow, the middle class drives and the poor keep taking the bus, so faster buses have higher proportions of richer riders.
With that caveat in mind, what I mean when I talk about low-income riders is the distribution of origins and destinations. The various draft plans proposed by Transit Matters members all focused on serving lower-income neighborhoods. This is why it’s not such a problem that the N1 only goes as far as Davis Square: that is the favored quarter of the Boston area, and the areas cut off from service, such as Arlington, are rich enough that few would ride an hourly or even half-hourly bus. Additional decisions made based on this principle include,
- The N32/N39 route serves Hyde Park and not Roslindale. At equal incomes, I’d probably suggest serving Roslindale, which makes for a shorter route, and allows the route to use the extra time gained to get to Forest Hills via a longer route on Huntington and pass near Longwood. But incomes are not equal: Roxbury is much poorer than Longwood and Jamaica Plain, and Hyde Park is poorer than Roslindale.
- The N57 serves Boston College, which is middle-income but still poorer than Watertown.
- The N111 serves Chelsea, and probably would regardless of average incomes, but it could instead go parallel to the Blue Line, serving somewhat less poor and less dense areas.
The schedule’s importance is higher at lower frequency
None of the above principles really matters to a subway with 2-minute peak headways and 4-minute off-peak headways. Some of these subways don’t even run on a fixed schedule: it’s more important to maintain even headways than to have trains come when the nominal schedule says they will. The point where clockface scheduling starts to become important seems contentious among transit planners. Swiss planners use clockface schedules down to (at highest) 7.5-minute headways, and say that 11-minute headways are a recipe for low ridership. In Vienna and Berlin, timed transfers are offered on the U-Bahn on 5-minute trains. At the opposite end, hourly and even half-hourly services must be designed around a schedule with quick connections, to prevent passengers from having to wait the full headway.
In borderline cases – the 7.5-15 minute range – transfers can be timed, and at the less frequent end some overtakes, but there is no real need to design the rest of the schedule around the headway. The main reason to operate with tight turnarounds is to reduce fleet and crew requirements. Any looseness in the schedule, beyond the minimum required for punctuality and crew comfort, should be thought of as a waste. However, the waste is capped by the overall headway. Concretely, if your favorite transit route takes 31 minutes one-way after factoring in turnaround time and schedule padding, then it needs 2 vehicles to provide hourly service, lying idle half the time; to provide 10-minute service, it needs 7 vehicles, lying idle only 11% of the time. So if frequency is high enough, the route should be designed without regard to turnaround times, because the effect is reduced.
But NightBus is hourly; 30-minute service is aspirational. This means that the schedule is more important than anything else. Even if a single neighborhood feels genuinely screwed over by the decisions made to keep the routes at or under 26 minutes – for example, if Revere and Mattapan prefer service going farther out even at the cost of 70- or 75-minute frequency – good transit activists must think in systemwide terms. Maintaining the hourly takt throughout the service area is more important than North Revere and the last few hundred meters in Mattapan.
Ultimately, buses and trains are not all that different
There are major differences between buses and trains in capital costs, operating costs, reliability, and so on, leading to familiar tradeoffs. Even at medium-size transit systems such as the MBTA, frequent bus networks are convoluted and at times fully gridded, while rapid transit networks are invariably radial at least to some extent,. Buses also can’t consistently use timed transfers at high frequency.
However, there are many similarities, especially with small bus networks, which are designed around a pulse rather than a grid:
- Public transit works with transfers and central dispatching. This makes it better at pulse-based network than any taxi (including ride-hailing apps) or ride-sharing service.
- Vehicles are large – not to the same extent of course, but relatively speaking (trains in large cities, buses in small ones or at night). There’s less room for the everywhere-to-everywhere one-seat rides that taxis provide at higher cost. If there’s budget for more service-hours, it’s spent on higher frequency or longer routes and not on adding more one-seat rides.
- Routes are centrally planned, with decisions made about one area affecting service in other areas. It is not possible for routes to evolve by private spontaneous action except in the thickest markets, far bigger than what small bus networks can support.
- The importance of the schedule and of timed transfers is proportional to the headway, and inversely proportional to frequency.
This is good news, because it means that the large body of good industry practices for rail planning, inherited from such countries as Switzerland and Japan, can be adapted for buses, and vice versa. I did not invent the principle of running trains as fast as necessary; it’s a Swiss planning principle, which led the country to invest in rail just enough to enable trains to go between Zurich, Basel, and Bern in one hour minus turnaround and transfer time. Nor did I expect, when I started getting involved in Transit Matters, that this would be so helpful in designing a better bus plan.