Friday, January 11, 2013

Understanding bus RPI

The MBTA quietly added a feature to their website called "Bus RPI" which you can also access from a link at the bottom of the homepage. These "Route Performance Indicators" are essentially the same data as the Biennial Service Plan but should be updated more frequently. The current RPIs only include a subset of the information about each route that the Service Plan did, but hopefully that will be changed in the future. The intention of this release is to be more open about the service planning and scheduling process that goes on at the T.

Route Number, Route Description: these are fairly self-explanatory, I hope.

Route Type: divided up into Local, Key, Community, Commuter, Express or NA. The main importance of this field pertains to the goals that each type is expected to meet. There is also a difference in "average fare paid per passenger" for the different types. Under pre-FY2013 budgeting, the average fares are as follows:

  • Local, Community and Key routes: $0.76
  • Commuter routes: $2.15
  • Express routes: $3.08

Average fare is computed by dividing the total revenue for all routes under that type by the number of riders of that type. It is smaller than a single ride cost because of numerous discounts, including senior, student and monthly passes. CTPS projections of the impacts of last year's fare increase seem to indicate that the new average fares will be approximately 23-24% higher, e.g. at $0.94 for local routes, but we won't know for sure until more data is released. Note that SL1, SL2 service counts as Rapid Transit for average fare purposes ($1.39) but SL4, SL5 receive the local bus average fare per passenger.

Net Cost per Passenger: This number is calculated by taking the difference between operating cost and revenue and dividing by ridership, for each route. However, revenue for each route is computed by taking the average fare for the route type and multiplying it by ridership, so it is not actually revenue that is specific to that particular route. In other words, Net Cost per Passenger is really operating cost per passenger minus average fare.

A common confusion with this metric is that it represents an amount that each additional passenger costs the T. That's not what this means. Take the popular route 1 bus which has a net cost per passenger of $0.63. If I decide to wander down to Mass Ave and hop on the bus, it does not cost the T an extra sixty-three cents. Instead, the T has invested approximately $18,500 dollars on a typical weekday to operate the full schedule of route 1 service. There are normally about 13,300 riders on a typical weekday, giving the net cost of (18,500 / 13,300) - 0.76 = $0.6309. Now add my trip to that total, and you end up with (18,500 / 13,301) - 0.76 = $0.6308, an ever so slight reduction in net cost per passenger. Bus service is a fixed cost, the net cost per passenger is the fixed amount distributed over all the users of the service, that's all.

The astute may notice that some routes have negative net cost per passenger. For example, the SL5 is ($0.03). This is a good thing, but once again, for the same reason, it shouldn't be treated as if each additional rider is profiting the T by three cents. It should also be noted that there are additional costs besides operating costs, which are computed by a formula which only factors in revenue hours and revenue miles.

The net cost per passenger metric is best used as a comparison between MBTA bus routes to see which ones are efficiently and effectively serving customers.

Service Delivery Policy Standards: A set of requirements for frequency, span, crowding, and cost which are more fully outlined in the Service Delivery Policy. Basically: is the service decently usable, and is it not costing us too much?

Ridership Info: This includes both daily (weekday) ridership, as up-to-date as currently available (seems to be 2010) and average rides per trip. The ridership numbers are not from the farebox, so they should reflect real ridership including people who show their passes and don't interact with the automatic fare collection machinery. The average rides per trip is simply ridership divided by number of (one-way) trips, which is intriguing, but the numbers currently shown are actually junk due to an error in formatting. Hopefully that will be remedied in the next RPI release.

Thanks to the MBTA's scheduling team for getting this data out, hopefully it will be expanded in the near future. I'm also looking forward to the next edition of the Blue Book.

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