Thursday, June 19, 2014

Why an Alewife commuter rail stop is a mediocre idea, and a plea for frequency

       In several recent conversations involving Cambridge's developing master plan, I've heard references to an Alewife commuter rail stop as a possible solution for the highly car dependent Alewife area. I think it's a decent idea, especially when combined with a pedestrian overpass, but the current MBTA commuter rail operating practices make it unlikely to generate significant ridership. Fundamentally, it comes down the the concept of frequency, and what makes transit useful.

Frequency: The great decider
When it comes to what makes people ride transit, one of the most common perceptions is that the service provided, in terms of physical infrastructure, determines ridership. For example, in a situation where a light rail line replaced a bus, ridership can be assumed to rise. This perception is partially correct, in that a totally equal service provided with Bus Rapid Transit and full Rapid Transit will experience higher ridership with the steel wheel version. However, there is a far more important characteristic determining ridership, which is essential to understand the poor performance of commuter rail in the United States.
First: Commuter rail ridership
In order to make my argument, it's useful to look at ridership figures for the commuter rail, using the MBTA's invaluable Blue Book. In particular, lets look at Porter Square, which is an "Outside the core" station with both commuter rail and subway service, in addition to several bus routes. If the hardware behind the service determines ridership, we should reasonably expect to see the comfortable, speedy commuter rail in first, more than one thousand riders spread over multiple routes. However, in reality the opposite occurs. By far the most popular mode is the subway, followed in a distant second by buses. In an abysmal third comes the commuter rail, with an absurdly small 250 inbound boardings.
What's happening: Frequency
With these numbers in hand, it would be useful to find a new new deciding factor, one that would predict Subway->Bus->Commuter Rail at Porter, rather than Commuter Rail->Subway->Bus. It comes in the form of frequency. Instead of looking at speed, we need to look at time to access: how long one person needs to wait before transportation arrives, whether it's in the form of a train, bus or rickshaw. In addition, we should look at service consistency: the knowledge that at any time of day, that person could show up and expect transportation quickly. A subway is the ideal model of this, and commuter rail does heinously. When you show up at a Red Line station, you know a train is coming in a maximum of ten minutes (unless the MBTA has discovered a new way to break down, but I digress), and importantly, you know that will be true all day. In stark contrast, the commuter rail has no such guarantee. If you arrive in rush hour you may have to wait "only" twenty minutes, but if you arrive in the middle of the day, you may have to wait for up to two hours. If you need to get somewhere in a hurry, the commuter rail is exactly what you don't want: long waits that you cant predict, short of memorizing an entire timetable. This creates a situation where only 250 people decide to ride the commuter rail, where at least 12,000 choose to ride more frequent, yet less comfortable, modes.
What this means for Alewife:
So what does this mean for Alewife? The short answer is, don't expect great, or even good, ridership for any new commuter rail stops. The long answer also includes a hint for what we should do: increasing frequency, even without superior modes, produces disproportionate increases in ridership. Therefore, a better idea to increase transit ridership at Alewife is perhaps the most basic: better frequency, measured by the mean time between a bus departing a stop and the next one pulling in. For frequency, a great general rule can be described by who a given headway is useful for.
1 hour: Useful for almost no one
30 minutes: Useful for students and the poor
15 minutes: Useful for those without a car
10 minutes: Causes people to leave the car at home
5 minutes: Causes people to leave the car at the dealership, unsold
You'll notice the most dramatic effect occurs at five minutes, exactly the Red Line's average frequency.


  1. Ted,

    Thanks so much for posting this insightful analysis. Regarding how the success of a new station is related to the frequency of service, I believe you have a legitimate point. I really love your final bit that correlates how long a person needs to wait for service with how likely they are to change their transportation choices.

    One thing that I would point out, however, is that there is another factor at play that can increase how attractive trains and other public transit options are to users, and that has to do with the advent of real-time location data related to both bus and train travel.

    The MBTA has a great app called Catch The T (and another called CatchTheBus) which provides real-time updates about arrival times. This means that I don’t need to stand around at the train station or the bus stop waiting for an eventual arrival, but can instead time my departure from home to coincide with the precise arrival of a train or bus. Similarly, I can quickly find out when the next train is due to arrive, even in situations where I don't know the train's regular schedule.

    This has definitely made bus travel in Boston much easier, especially in situations like the 86 bus from Central Square to Sullivan Square that only runs every 45 minutes. In the past, you might stand around at a bus stop for up to an hour wondering whether: 1) the bus was running late and you needed to simply wait a few minutes; 2) the bus was so late that they skipped a bus (known to happen frequently on that route) and a longer wait was required; or 3) the bus had actually arrived early, you had just missed it, and you should probably just get a cab or make the long walk to the T. This problem made it very difficult to coordinate efficient trips, especially if you had to be somewhere at a precise time.

    Now, with the buses and trains constantly transmitting their positions, I can make smarter choices about what mode to take and when. My expectation is that this ameliorates some of the pain of having a train that only comes infrequently, particularly in cases where you have riders unfamiliar with the regular schedules of such trains and buses.

    Just my two cents. Steve Kaiser might have another opinion. Regardless, thanks for bringing up one of the limiting factors that we will need to address if we are to improve the attractiveness of new transportation options.

    -Doug Brown

  2. That's a good point, and I certainly agree that ride tracking makes both public transit easier in the general sense and in the specific case of low frequency services, but it still leaves something to be desired. Knowing where a bus is dosen't help it get to you any faster (obviously) (although in your case it may *feel* faster, which is actually just as important), and what a headway measures is essentially how long you need to wait before you can get to the place you want to be. Filling that time with something more useful or enjoyable than sitting on a bench is a good thing, and will definitely help the lives of the aforementioned riders of the 86 and other low frequency bus routes, but it's still time spent *not where want to be*, which is the crux of the problem.

  3. The point of a commuter rail station at Alewife would not be to get people to North Station, it would be to get people from further out on the line to Alewife (which is what Porter is mostly used for as well). In particular, even with the terrible frequency, it would be pretty convenient for commuting from Waltham, and from father out along the Route 2 corridor as well. In the case of Waltham, the alternative transit route (via the 70 and Red Line, or even 70, 71, and Red Line) takes a really long time, and the double transfer considerably increases delay risk too. Trading a nearly hourlong oddyssey for a 10 minute ride is a huge win even with terrible frequency.

    1. That's a good point, but because of the ease of Porter as a transfer stop between CR and Red, and the distance involved between the tracks at Alewife and any entrances to the T, I think the new station will attract people who work at Alewife and pretty much no one else (very few transfers to Red or Busses). Unfortunately, as useful as that is for Waltham residents, the cost of accommodating the (hundreds?) of riders would be, as quoted to me, $15 million. My argument is that, given the 15mil, we would be better off simply improving the frequency on the 70 or 71, and, to reference my other post, implementing BRT on Concord Ave.

  4. There's another aspect worth mentioning: does it get you where you want to go? The inbound CR goes only to north station. To go anywhere from there not in walking distance you have to pay again. Once on the subway you can connect to any other subway, to any bus, and go all over the city, with no transfer penalty, and usually easier connections.

    1. This is true, and the first step in making the commuter rail useful for rapid transit MUST be to implement charliecard payment with free transfers. However, we can also see the described characteristics with the Braintree branch of the red line, where both the subway and commuter rail are going to the same place (the CBD).