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The art and science of a short turn

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This post has been a long time coming. A while back I asked people on Twitter if they would be interested in a post about bus bunching and short turns (answer: a resounding yes) and have been stewing on it for a while. I’ve gotten some feedback that this post is too long, so if you don’t care (and it’s quite possible that you don’t) feel free to skip and read something else. Thanks to my coworkers for looking this over and giving feedback, and the bus drivers on the service who executed the short turn.


A bit of background: in my day job, I work for the Charles River TMA. One of the programs we manage is the EZRide shuttle: a small, last-mile commuter shuttle between North Station (major transit node) and Kendall Square (major employment center). The service has been around since 2002, is mostly funded by local employers and property managers, and sort of serves as another branch of the CT buses, connecting North Station, Lechmere and Kendall. We carry about 2500 passengers per day, and are near or at capacity at peak hours (7:45 to 9:00 AM, 4:15 to 5:30 PM). Most of our ridership is comprised of Commuter Rail riders who work in Kendall. The shuttle is free to corporate members and open for a cash fare to the public.


For the purpose of this blog, I am italicizing certain transity jargon and defining them at the end of the article. Our organization contracts the route to a private operator, and we both have dispatch duties. As it breaks down, they mainly deal with driver issues (broken down buses, drivers needing time off the bus, work schedules) and we keep an eye on passenger issues (loading, bunching, headways).


Our route sometimes allows us short turns, especially when there’s bad traffic, but that successfully implementing a short turn takes a lot of know-how, and a bit of magic and luck. Some short turns are relatively easy: two buses are running back-to-back, the first bus as 33 passengers and the second bus has two. (This sort of bus bunching—here’s the best resource on that from WBEZ—is all too frequent on busy routes, even when buses run at a scheduled, even headway.) If we can empty the second bus on to the first, we can turn the first bus back to fill a gap elsewhere on the route. This only works if there is a need precipitated by traffic, but that is often the case.


Since many people have asked (okay, maybe a couple people) for a description of a short turn, here is one, with way too many words, and a bunch of maps, too. A follow-on post talks about locations where the MBTA could implement short-turns.


*****


The Route


A short turn doesn’t just happen. It comes about from a unique set of circumstances, deep knowledge of the route, traffic, passenger loads, the weather, an innate, built-up sense of what the route looks like and how it will be affected by traffic and loading in to the future. Sure, there’s some luck thrown in, but most of that is self-made: a well-executed short turn should be more science than art—it just feels like luck when it works. (And it doesn’t always work; rule number one, before you even consider a short turn, is to try to at least not make things worse.) I’ll describe a recent short turn success, and the elements that go in to it. The whole of the operation, from diagnosis of the problem to the successful implementation of the turn, took about 12 minutes—likely shorter than it will take you to read this blog post.


We have separate morning and evening routes, due to passenger loading (our reverse-peak carries MIT students) and one-way streets. The route map can be found here, and our route in Nextbus’s interface here. The route requires several routes and jogs, mostly due to one-way streets, and it’s prone to traffic, especially during construction. Our evening route can be roughly divided in to four segments, each of which takes about 15 minutes, with 16 minutes of recovery time as follows:

Inbound:
Cambridgeport to Kendall Square (moderate commuter ridership, minimal traffic delays)
Kendall Square to North Station (heavy commuter ridership, moderate to heavy traffic delays)
[12 minutes of schedule recovery time (necessary due to traffic)]
Outbound:
North Station to Kendall Square (minimal commuter ridership, moderate traffic delays, although heavy recently)
Kendall Square to Cambridge (moderate student ridership, minimal to moderate traffic delays)
[4 minutes of schedule recovery time at Cambridgeport]

*****


The Situation


On Thursday, April 9, we had some operational issues. Due to traffic signal timing problems, O’Brien highway backed up, and we experienced a 10 to 12 minute delay on our outbound route (this section carries very few passengers at this time of day, but it is necessary to get our buses from the terminal back to the start of the route). On a nice day, we might have some buses operating empty outbound through Kendall Square, but with cold rain on April 9, we had no buses which were empty and could be rerouted, so we couldn’t deadhead a bus to the terminal, or an intermediate part of the route.


The scenario was to the point where we had a 15 minute service gap. This is not good for a few reasons. First, this is double our scheduled headway is 8 minutes, so this was nearly double our schedule, even if it means that waits will only be a few minutes longer. But the issues would cascade: the first bus to pick up during this gap would fill up well before the end of the route, meaning the headway for later stops would be longer and would wind up being based on the headway of the second bus, so it would wind up being more in the 18 to 20 minute range.

And then: the bus that was supposed to run called in with a mechanical failure. All of the sudden, 7 of our 9 buses were on the outbound route, and we were facing a 20-24 minute service gap. In other words, we were screwed. Here’s the setup:

The arrows show the inbound route, and the red dots show the major passenger generators at this time of day (peak rush hour); as you can see that there are no inbound buses between the west end of the route and the eastern terminal (just off of the map) except for bus 9901, which is most of the way there. (Ignore the times “late”; we’d already had some delays to this point.) Bus 711, shown in gray, is broken down. And the driver of bus 708, at this point, got off his bus to try to diagnose the issue of 708, and due to radio traffic we were unable to tell him to get on his [goddamn] bus and drive the [goddamn] route.

So now we had a problem. 706 caught 708. We needed a bus to run the route, but expected it to fill up before it could board all the waiting passengers, especially at the three red dots. It also coincided with the peak loading time for our route, when even under normal operations buses can load to capacity and leave riders behind. We could send a double draft to run the route, but then the second bus would wind up empty behind the first bus as it boarded passengers (most of our route is too narrow to safely pass) meaning that the passengers later in the route would have a longer wait. While I was yelling at no one in particular about 708 (in our office, using curse words) my boss (who has been watching this route for more than a decade: that’s institutional memory) mentioned that we could deadhead 706. What a splendid idea—as my ire grew with 708 for attempting to fix a broken down bus and not just covering the route I hadn’t noticed this possibility. (To be fair, the driver of bus 708 probably didn’t realize the situation on the rest of the route.)


*****


The Operation, or, the Rules of the Short Turn

Rule #1 of the short turn: Don’t Make Things Worse


The first question to ask in a short turn is: will this actually make much of a difference, and might it make things worse? If you are going to move heaven and earth to get a bus somewhere 90 seconds earlier, it’s much easier to just have buses run the regular route. Unless you can solve a loading issue and a headway issue together, it’s rarely worth doing. (A service gap in a non-peak direction affects many fewer passengers than in the peak.) The second question is: will this short turn now cause more problems later? If the answer is yes (and quite often it is), you have to weigh how severe of a problem it will be, and when it will occur. Can you solve an inbound issue at 5:15 that creates an outbound service gap at 6:15? Fine, better to improve the ride for 50 riders and inconvenience a handful at a much less busy time. If you can get two people off of the second of a bunched pair and on to the first, turn the empty bus and cut the wait time for two dozen, totally worth it. But if you’re trading off a delay for three people now versus a delay for five people later, it’s not worth doing. 


In this scenario, we were not going to inconvenience anyone, really, and improve service for a lot of people (and get buses better spaced in to the future). It was a no-brainer.



Rule #2 of the short turn: Know Your Route.

If you’re running a short turn, you need to know your route. You need to know where a driver can go around a block easily, or where they might get stuck in traffic (or worse: a tight corner not suited to a 40 foot bus, a frequent problem in Boston). Before you can do this kind of active dispatching, you have to know where you can safely and expediently turn a vehicle. It helps to have twenty-plus years of dispatching in the other two members of my office (I’m the new guy): they’ve been through everything. Construction detours, full road closures (the Craigie Bridge reconstruction), never-ending blizzards (okay, that was this year) and the like.


Due to the one-way nature of Kendall Square, the route does have a bizarre loop built in, which takes a couple of minutes to traverse but accesses a major stop. So one idea would be to deadhead bus 706 and have him run out of service (and preferably off-route down Main Street to Ames: nothing makes passengers angrier than seeing an empty bus drive by without stopping) and pick up at the last red dot on Broadway. If he got there expediently, he’d be able to at least pick up at that stop—and ensuing stops—and mitigate the service gap there, and take on the passenger load the first bus, 708, would not be able to pick up.


Rule #3 of the short turn: Be Invisible.


To passengers, at least. The best short turn is one where the deadheaded bus doesn’t pass any passengers waiting, where no passengers are asked to leave the vehicle, and where, except for the driver and the dispatcher, no one knows. This could also be phrased as “don’t piss off the riders” which is always a good policy: sending an empty bus past waiting passengers is a recipe for angry calls and emails. Generally, we operate under a policy of transparency with riders (we will suggest alternate transit means during especially bad traffic, for instance—it’s beyond our control but our goal is for our passengers to get where they’re going, not to boost our ridership), but we don’t feel the need to describe every piece of our operation. In the case of a short turn, we might send out a Tweet such as “Service gap inbound due to residual traffic delays and disabled bus. We will attempt to redirect service to fill this gap” usually suffice.


Rule #4: Know your Drivers

Now at this point it is worth pointing out that that you really need to know your drivers when juggling buses in this manner. Some of the drivers on our route could dispatch themselves: they have an innate idea of where every other driver is on the route, what their scheduled times are, and what their likely traffic and passenger load impacts will be. (Another recent night, two long-serving drivers basically rerouted each other and other buses, on the fly, to avoid traffic and fill route gaps far better than I could have even while staring a map of the bus GPS locations.) Other drivers are newer to the route and may not know the vagaries of Cambridge’s off-route street grid, and need a lot more guidance across the route. In this case, the driver of 708 is somewhat newer and knows the route fine, but harder to manage: we were happy that his only instructions were to run the regular route. The driver of 706 is one of our best and has been driving the route for a while; a simple instruction like “deadhead to Main Street, left on Ames, first pickup on Broadway” would be all that he’d need.

So that’s what we did. Bus 708 would run the regular route making all stops, and would likely be full at Kendall Square. (The buses we currently run are 35 foot buses with 32 seats and a stated crush load of 45, although more passengers have been known to cram aboard.) There was no point holding 706—we had another outbound bus behind him—so we sent him to do the pick-ups beyond Kendall, but to take a direct route there, leapfrogging ahead of 708 and shortening the wait at the subsequent stops (and we expected him to fill up at those stops). 708 would then run by those stops a couple minutes after 706, so would have fewer passengers to pick up. 


Rule #5: Pay Attention.


But the operation isn’t over until the buses are back on the regular route, drivers know future departure times, and they have recovery built in to get back to normal. So far, everything was going according to plan, but you have to pay attention to a short turn until it’s on its way to a logical conclusion. 706 had made good time on Brookline Street and had chosen an appropriate, off-route path for his deadhead; again, had this bus passed a group of long-waiting passengers, they’d go from irked to irate. 708 was serving some moderate-ridership stops, and headed towards Technology Square, where he’d take on many more passengers. 

#Protip: if two buses are coming together, take the second one. It’s unlikely to be any slower (it might actually pass the first bus) and you’re more likely to get a seat.

Anyway, the plan was working, rather swimmingly. And then: nirvana. See how, above, bus 707 is catching up to bus 709? While this is not a busy part of our route, but on a rainy day, there are some passengers who will take a circuitous bus ride to Kendall rather than make the walk. So while bus 709 was stopping for a rider here an there, 707 wasn’t, and he radioed in that he was behind bus 707, and was empty. Bingo. We were worried 708, upon reaching Kendall Square, would be too full for the boardings there. But 707 could conceivably balance the load between three buses as long he was slotted in before 708 reached Kendall. Each of the main passenger nodes would get its own bus, balancing the load well. If it worked. It was worth a try.



But remember: you have to know your drivers. 712 is a driver who had recently bid on to our route, and had had some issues with the route (not entirely his fault: our route flips based on the time of day—since we serve students and commuters in separate directions—and can be confusing for both riders and drivers to learn, although once familiar, it works quite well) and certainly didn’t know his way around Cambridge. In other words, if he’d been in 706 a few minutes earlier, it’s doubtful we would have sent him on the deadhead in the same way we did 706.

Somehow this worked.
But we could coach him through it. 706 and 708 had their charges, and the radio channel was clear. So the call went out. “707: take a left on Broadway, then proceed straight down Main to Third Street. Make a right turn there, and make your first pick-up at Kendall Square.” We’d have to watch him like a hawk and keep in radio contact: if he missed the turn there, at best we’d have to coach him on to Memorial Drive, and on to the outbound route (a portion of our route uses Memorial Drive, and our drivers have never missed the turn and gotten stuck under the Mass Ave overpass). At worst, we’d lose him across the Longfellow for half an hour. (Don’t laugh. This has happened.) The short turn can be dangerous.

And it worked! 707 made the short turn in to Kendall and instead of following 709 on the outbound switched to the inbound. Astonishingly, we had evenly spaced the buses with about 3 minutes between each, which is particularly impressive since that meant that 706 was now 6 minutes—nearly a full headway‚ ahead of 708, who had left the route terminal behind him! And both 706 and 708 were nearly full, so bringing in 707 kept bus 708 from reaching Kendall, filling up there, and then reaching the next stops later, with more passengers to pick up, filling further, and perhaps leaving passengers behind. Much of the credit goes to the drivers, who let us know their situations (when they were empty and bunched) and were willing to jigger their routes in order to balance the load. The fact that such reroutings are not infrequent means that they’re used to being asked to do so, and that they execute the maneuver well.

Once the buses had all made their way on route, we actually had well-spaced buses. In fact, 706 and 708 were a full headway apart at this point: had we not deadheaded and short-turned they’d both be where 708 was, and we’d have cascading issues as they both ran into and then out of the terminal late. (Often, a headway issue at 6 PM can be caused by a traffic jam at 3:30.) But the pieces of the puzzle had fallen in to place, and the short turn had been executed, successfully. 

This is pretty much what our map should look like in normal service. (Well, except that the buses were way off their originally scheduled runs, but if I look at the map and every bus is 20 minutes late, that means that we have even headways and just had some issue earlier on.)


As my boss said, it was ballet. It was all over in about 12 minutes. But the best part? We had the buses in numerical order: 706, 707 and 708. Boom.


*****


The Aftermath

Why “art and science (but mostly art)”? It’s often suggested that computers could do this better than people, and why do transit agencies employ dispatchers, anyway, since an algorithm would do a better job? But that assumption is flawed for several reasons. First of all, unless an algorithm has nearly perfect ridership data, someone familiar with the route will have a better idea of where and when stops have heavy demand. Second, an algorithm would have to be able to not only know that a deadhead route will have less traffic at a given time than the normal route, but also communicate that route to the driver (and, frankly, I don’t find Waze and its ilk that useful at the block scale). And the algorithm would have to know which buses were full and empty: passenger counters are not perfect, but a driver can pretty quickly and easily respond to a radio call of “do you have any passengers?”

But the fundamental issue is that this type of service is dealing with people, both drivers and passengers. It’s pretty easy for a person—with some knowledge of the route—to balance out which stops to serve, and in what order, and what stops to prioritize. Maybe you’re a bit less concerned with Kendall Square because it has a shelter, so a minute or two longer there isn’t a problem. Maybe you know that given the weather one stop is more likely to be used than another because it has an overhand or an alcove for people to stand at. Maybe you know one driver is able to navigate the route faster than another (we have one of these: he drives safely and smoothly, but knows the route so well he regularly covers it faster than any other driver), while another is slower. Maybe one bus is balky and you don’t want to push it lest it break down.


Certainly you don’t want to deadhead an empty bus past a full bus shelter, or incur the wrath of customers who—even if you are doing it for the benefit of the service—would be understandably upset. And it’s also important to know your drivers, know what they are capable of, and talk them through what they need to do. Because despite all the talk of autonomous vehicles and hyperloops, right now and for quite some time to come, buses are driven by people and carry people, and despite various limitations, there are certain things where the Turing Test is still yet to be achieved.


A subsequent post will discuss routes where the MBTA could potentially use short turns to mitigate the effects of bunched buses.

Glossary:

Deadhead: run an empty bus without stops, and possibly on a more direct route.
Headway: the time between buses.
Double draft: two vehicles running together; more of a train term coopted here.

Don’t use bus routes to subsidize malls …

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… especially if the mall isn’t the final stop on the route.

I recently had the pleasure of riding the entire route of the 34E, one of the MBTA’s longest bus routes. The route starts in Walpole Center, makes a beeline to Washington Street (which extends from Boston to Providence) and runs in a straight line to Forest Hill Station. A straight line, that is, except, for a bizarre figure-eight loop through the Dedham Mall. The loop-the-loop to access the mall unnecessarily lengthens the route, costs the T money, costs passengers time, and subsidizes private development, all to service the front door of an auto-centered development.

Instead of continuing on Washington Street, the mall loop takes 8 or 10 minutes as the bus leaves the street, navigates no fewer than eight stop signs and traffic signals, makes two separate looped turn-arounds and traverses the same intersection three times. The route is scheduled for a full hour for the 14 mile trip from Walpole to Forest Hills, so the detour through the mall accounts for 13 to 16% of the total run time, all to serve two stops (out of more than 80 total on the route) which would otherwise require a 2 to 5 minute walk.

In other words, for riders wishing to get to the Dedham Mall, it would likely be faster if the bus ran straight on Washington Street and they got off and walked in to the mall, rather than taking a circuitous route to be dropped near the door. And for everyone else, it would save 8 to 10 minutes each way of not riding through the mall parking lot.

I rode the route on a weekday evening a few days before Christmas. This should have been a high water mark for people using the 34E to get to the mall. While my bus was full—there were probably between 45 and 50 passengers on board at any given time (and probably 70 or more served along the route)—only two or three got on or off at the mall. So, in order to serve this small number of passengers, the rest of the bus had to loop in and out and in and out of endless parking lots and driveways, because front-door service to the mall is apparently required.

From HumanTransit.org

What is particularly irksome is that in this case—and it’s not isolated, but, at least in Boston, perhaps the most egregious (the 350 serves the Burlington Mall with a similar detour, but much closer to the terminus of the route, meaning that many fewer passengers are inconvenienced by the route’s detour)—is that anyone who rides the bus past the mall has their trip dramatically lengthened (how dramatically? 18 minutes a day, five days a week, 50 weeks a year adds up to 75 hours of extra time on the bus annually). Jarrett Walker talks of “being on the way” and the mall is decidedly not; the 34E takes what should be a straight-line transit trip and degrades it to a mall circulator, despite the thousands of passengers who ride the bus daily.

In addition, running service via the mall requires several hidden subsidies which degrade service and provide a perverse incentive for people to drive instead of use transit. This one, in turn, further subsidizes the car-centric mall over pedestrian-oriented business districts, several of which are served by this route. There is also the direct subsidy to businesses at the mall. If I open a store on a street near an existing transit line, I would not (and should not) expect the transit agency to reroute the transit line to provide a stop at my front door. Yet we provide this service to the mall.

This subsidy can be quantified, in fact. The T doesn’t break down service between the 34E and the 34, but let’s assume that slightly more than half the passengers on the route are carried by the 34E (looking at the total number of vehicles on the route at different times of day)—or about 2500 passengers. The route costs $3.09 per passenger to operate (66¢ average bus fare paid plus $2.43 subsidy), or a total cost per day of about $7725. If we calculate 15% of this approximately $1150, meaning that over the course of a year—even given lower service levels on weekends—the cost to serve the mall is well north of $300,000 per year. [Update: these numbers may be somewhat lower given that morning service—before the mall opens—and some peak evening rush hour trips do skip the mall.]

Here’s another way to look at this: currently, the 20 minute evening headways on the 34E requires 6 buses running the route in about (or just under), each bus makes a round trip in two hours. If the run time were reduced to 51 minutes by omitting the mall, the same six buses could make seven round trips, reducing headways and, thus increasing capacity on the route. If you could get it to 50 minutes, the same headways could be maintained with 5 buses, which would save 1/6 of the route’s operating cost while providing the same service. But, instead, we provide service to the mall, at the expense of everyone who isn’t the mall.

What to do? Make the mall subsidize the route—yes, to the tune of $350,000 per year—or have them build an ADA facility from Washington Street to the mall. The extra cost of running this route in to the mall for 10 years could buy a very nice set of bus shelters, crosswalks and a ramp from Washington Street to the mall’s front door. Another option would be to run the 34—which ends its route nearby—to the mall, instead of putting this joggle in the middle of the 34E. While it might not have the same cost savings, it would at least not have the effect of costing thousands of passenger hours each day. Or, abandon service to the mall all together. Malls are dying, anyway, and it should not be the business of public transit agencies to help prop them up.

The 70 bus is just … bizarre

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The Boston Globe carried a story this week about Watertownies (Watertownians?) who want better MBTA bus service. Watertown is one of the furthest-in, densest communities in the Boston area with only bus service, and residents want improvements. Residents of Watertown are asking for more buses at peak hours (the T doesn’t have the vehicles to provide this), faster service (perhaps they should invest in bus lanes) and better services overall.

There is particular sentiment about improvements along the Arsenal Street corridor, which is served by the 70 bus. And the 70 bus is one of the most interesting routes in the MBTA system, and one which could certainly stand to be improved. In fact, it’s bizarre, a compilation of several separate routes, and it seems to have taken place haphazardly. The route is one of the longest in the system, and its headways are such that while it may operate on average every 15 minutes, there are frequently much longer wait times, leading to crowding, bunching and poor service levels.

The T claims to want to study the route, but can’t come up with the $75,000 to do so. We here at the Amateur Planner will provide a base analysis (for free), in hopes that it can be used to improve service on this route. One concern in the article is that “There are people waiting 40 minutes for a bus that’s supposed to run every 15 minutes.” Unfortunately, this is not an isolated occurrence based on equipment failures and traffic, but rather the fact that the 70 bus route is set up with uneven headways which mean that a bus which is supposed to come every fifteen minutes might actually have schedule gaps much longer. It’s a complicated story, but fixing the 70 bus should be a top priority for the MBTA.

I. The Route

The 70 bus was, like most bus lines in Boston, originally a streetcar line, much like the 71 and 73, which still run under the wires in Watertown. When the 70 was converted from streetcar to trackless in 1950 and from trackless to diesel ten years later, it was much like any other MTA route. It ran along an arterial roadway from an outlying town center (Watertown) to a subway station (Central), a similar distance as, say, the 71 or 57 (a car line until 1969) intersecting it in Watertown Square. But after that point, it’s fate diverged. Most other lines continued to follow the same routes they always had. The 70, however, absorbed services of the Middlesex and Boston, leading to a much longer route. As time went on it was extended to Waltham (in 1972, combining it with the M&B Waltham-Watertown line) and then to Cedarwood. The 70A routing was only merged in to the route in the late 1980s when through Waltham–Lexington service was cut, adding a third separate line to the 70/70A hodgepodge. (More on the history of this—and every other MBTA route—here.)

It now extends—depending on the terminus—10 to 14 miles from Central Square in Cambridge to nearly the Weston town line. Along the way it serves several distinct activity nodes: Central Square in Cambridge, Barry’s Corner and Western Avenue in Allston, the Arsenal Mall, Watertown Square, Central Square in Waltham, and the outlying branches. While these nodes fall in a straight line, it creates a bus route with several loading and unloading points and heavy use throughout the day. This is not a bad thing—except that the line is poorly scheduled and dispatched, so that it effectively provides far less service than it could.

II. The Schedule


To its credit, the MBTA has very few split-terminus routes. (In many cities, split-terminal routing is the norm, as one trunk route will branch out to several destinations. Since MBTA buses generally serve as feeders to rapid transit stations, it is far less prevalent.) The 34 has short-turn service (the 34E) and the 57 has some short-turns as well. A few other routes have some variations (the 111, for example) but few have the sort of service that the 70/70A has. The 70A is particularly confusing inasmuch as the morning and afternoon routes run separate directions, to better serve commuters but to the detriment of providing an easy to understand schedule. It it almost as if the T has put all of its annoying routing eggs in one basket. Or, in this case, in one route.

The issue is that while there are two routes which are generally separately scheduled, for the bulk of the route, from Waltham to Cambridge, the operate interchangeably as one. For someone going from Waltham to Cambridge or anywhere in between, there should be no difference between a 70 and 70A. If there are four buses per hour, there should be one every fifteen minutes. For those visiting the outside of the route, the buses will be less frequent, but for the majority of the passengers, it wouldn’t matter.

Except, the route doesn’t work this way.

It seems that the 70 and 70A are two different routes superimposed on each other with little coordination. This often manifests itself in buses that depart Waltham—and therefore Watertown—at nearly the same time, followed by a gap with no buses. If you look at nearly any bus route in Boston, it will have even (or close-to-even) frequencies during rush hours. Some—the 47, for instance—may have a certain period of time with higher frequencies to meet demand. But even then, the route quickly reverts to even headways.

This is not the case with the 70 bus. If you are in Watertown Square traveling to Cambridge on the 70, there are 16 buses between 7 and 10 a.m. This should provide service every 10 to 12 minutes. Here are the actual headways (the 70As are bolded):

16  7  9  9  6  13  8  12  8  24  0  24  5  15

Anyone want to point out the problem here? The headways are completely uneven. The route is frequent enough that it should be a “just go out and wait for the bus” but it is completely hamstrung by poor scheduling. The initial 16 minute headway will carry a heavy load—nearly twice the headway of the next trip. The next trip will operate with half the load, and more quickly, catching up on the heavily-laden bus ahead of it. Later in the morning it gets worse: headways inexplicably triple from 8 minutes to 24, followed by two buses scheduled to leave Watertown at exactly the same time. (In fact, one is scheduled to overtake the other between Waltham and Watertown.) This is followed by another long service gap. Miss the two back-to-back buses, and you’re waiting nearly half an hour. This makes no sense.

And it’s not just the mornings. Midday headways are just as bizarre. When traffic is at a minimum and the route should be able to operate on schedule, headways range from 10 to 25 minutes. There are at least three buses each hour (and usually four) yet there are long service gaps—the effective headway is nearly half an hour when it could conceivably be 15 minutes. It’s obviously not easy to schedule a route with two termini, but the vagaries of the schedule mean that missing a bus may mean a wait of nearly half an hour, only to have two buses come with ten minutes of each other. And it’s not like these buses are empty, either. They serve the bustling town centers in Waltham and Watertown, and the Arsenal mall area stops regularly see ten or more passengers per trip. Yet they are subjected to a bus that comes at odd times—not one that is really reliable.

For a time during the evening rush hour, the T actually manages to dispatch an outbound bus every 10 minutes. But overall, most of the weekday schedule is a range of times which have no relation to each other, and mean that the route provides a much lower level of service than it could. (Intriguingly, Saturday service on the 70 is provided on an even 10 minute headway for much of the day; it’s a shame this schedule can’t be used on weekdays, too.)

I’ve been experimenting recently with graphically displaying route schedules. It shows scheduled route times as points, and headways as lines. Time of day is on the x axis, frequency and running time on the y axis. Here, for example, is the 47 bus:

Notice that while there is a major service increase during the AM rush hour, the headway lines are generally flat during different service periods during the day.

Another example is the 77 from Harvard to Arlington:

The 77 is a very frequent bus which sees 8 to 12 minute headways throughout the day. There is some minor variation at rush hours—and longer scheduled trip times at those times—but variations are minimal, and when headways change, they do so by only a couple of minutes.

Most bus routes have this sort of chart. Trip times may vary, but headways do not change drastically during the day.

Now, here’s the 70 from Waltham to Boston:

This is chaos! Instead of a flat line, the headways bounce around uncontrollably, ranging from one or two minutes (this is from Waltham, so the 0 minute headway in Watertown Square is slightly different) up to nearly half an hour. If you go wait for a bus you may see two roll by in the span of five minutes, and then wind up waiting 25 minutes for the next. It’s only during the evening rush hour (the flat blue line) that there is any order to the schedule; even late at night headways bounce around by five minutes or more.

Another way to visualize these data are to look at the average headway versus the effective headway. Here, the gray line shows the moving average of three headways, which smooths out some (but not all) of the variability shown above. However, the yellow line is more important: it shows the greatest of the three headways, which is the effective headway: if you go out and wait for a bus, it’s the maximum amount of time you may wind up waiting. Here’s the inbound route:

The average headway for bus is generally about 10 minutes at rush hours, and 15 to 20 minutes during the midday, which is not unreasonable for this type of route. However the effective headway is much worse. It is more than 20 minutes for much of the day—and often eclipses 25 minutes. For most routes, the average and effective headway would be equal (or close to it). For the 70, the effective headway is sometimes double the average.

The outbound chart shows what is possible. From 4:00 to 6:00 in the afternoon, the average and effective route are nearly even—this is when buses are sent out on equal headways (and this is what the entire day would look like for most routes). However, during much of the rest of the day, the headways are less sensible. It should be possible to operate a service every 20 minutes or better, but there are often 25 minute waits for the bus, despite the fact that the two routes share an outbound departure point in Central Square.

All of this does not align with the T’s stated policy. According to the MBTA service deliver policy, “passengers using high-frequency services are generally more interested in regular, even headways.” This is the practice for most routes, but not for the 70.

III. What can be done?


As currently configured, the 70’s headways are particularly hamstrung by the 70A. Not only is it longer and less frequent than the Cedarwood route, but it’s outer terminus is not even a terminus but instead a loop (with a short layover), so the route is practically a single 25-mile-long monstrosity beginning and ending in Central Square. Without a long layover and recovery point, the route is assigned two buses midday and can’t even quite make 60 minute headways: the 10:10 departure from Cambridge doesn’t arrive back until 12:11, and that’s at a time of day with relatively little traffic!

It’s also not clear why the 70A needs to run to Cambridge. It is a compendium of three routes—the original Central–Watertown car route, the Middlesex and Boston’s Watertown–Waltham route and the Waltham portion of the M&B’s Waltham–Lexington route. This is a legacy of the 1970s—and before. It would seem to make much more sense to combine the 70A portion of the route with one of the express bus routes to downtown Boston, and run the 70 as it’s own route with even headways.

There seem to be two reasonable routes to combine the 70A with, each of which could probably provide better service with the same number of vehicles: the 556 and the 505. The 556 provides service from Waltham Highlands (just beyond the Square) to Downtown Boston at rush hours, and to Newton Corner at other times. It has an almost-identical span of service to the 70A and operates on similar headways (30 minutes at rush hours, 60 minutes midday). Instead of running all the way in to Cambridge, 70A buses could make a slight diversion to serve Waltham Highlands and then run inbound to downtown. Currently, the 70A is assigned five buses at rush hour, and the 556 four. It seems that using two of these buses to extend the 556 to North Waltham would easily accommodate 30 minute headways, freeing up three buses to supplement service on the 70. During the midday, one bus could provide an extended 556 service between North Waltham and Newton Corner (where connections are available downtown), and it might be possible to extend run 60 minute headways between downtown and North Waltham with just two buses, allowing the other to supplement service on the 70, or allow for transfers to the 70 and Commuter Rail in Waltham and express buses in Newton Corner.

The other option would be to extend the 505. The 505 is currently a rush hour-only bus, but its span of service matches that of the 70A at either end, it is only from 10 until 3 that it provides no service. The simplicity with the 505 is that it’s current terminus is in Waltham Square, so it would be a simple extension to append the 70A portion to the route. The 505 currently runs very frequently in the morning with 10 buses providing service every 8 to 9 minutes, and has 7 buses running every 15 minutes in the evening. If every third bus in the morning and every other bus in the evening were extended to North Waltham, it would provide the same level of service as the 70A, but with direct service downtown. Midday service would be more problematic, as it would require two buses to operate, and additional vehicles would be necessary to supplement the loss in service on the 70 (although the T has a surplus of buses midday, so while it would require extra service time, it would not incur new equipment needs).

Either of these solutions would allow for 10 vehicles to provide service on the 70 route at rush hour, and they could be dispatched at even intervals during that time. With recovery time, the roundtrip for the 70 at rush hour is less than 120 minutes, so with ten buses it could easily provide service every 12 minutes, and perhaps be squeezed down to every 10 minutes with faster running time on the shoulders of rush hour. If every other trip was short-turned at Waltham, 10 minute service would be possible, with service every 20 minutes to Cedarwood. And the headways would be even—no more 20 minute waits in the middle of rush hour. Transfers could be made at Waltham for 70A patrons wishing to go to Watertown or Cambridge. During the midday, similar even headways of 15 or 20 minutes could be offered—no more long waits for a crowded bus with an empty one right behind.

Over the years the 70/70A has been cobbled together from a number of routes, and this has hobbled the efficacy of the route. While the exact scheduling of the route has to take in to account many other factors (pull outs and pull ins, union rules, break times, terminal locations and the like—and as someone who recently helped create a route plan for a very short route, I can attest there is more to route planning than meets the eye), it would be hard to make it any worse than it is now. With some creative thinking, the T should be able to provide better service for everyone who takes the 70 bus without expending any more resources, and should be able to increase the effective capacity, and make it a better experience for its customers.