A month and a half ago, when I wrote about a possible restructure of trolleybus service on the Queen Anne-Belltown-Downtown-First Hill-Madrona corridor, I promised “within a week” to explain why the restructure could deliver so much more service with roughly the same amount of money. Obviously, I’m several weeks late in doing this, but I hope you’ll forgive me.
To tackle this subject, I have to introduce a some planner jargon:
- Clock-face schedule. A schedule that attempts to place a bus at a stop at consistent times past the hour (e.g. :07, :27, :47 for a 20-minute headway service). For routes operating at headways longer than 10 minutes, these schedules are the most comprehensible to riders; at shorter headways, riders tend not to worry about schedules.
- Cycle time. This is the amount of time a bus takes to run a complete round trip and be ready to start out on the next trip. This includes driving time, required layover break time, and schedule padding, but does not include the deadhead time from the base to the starting point.
Let’s take a simple example. Suppose we have a route that takes 27 minutes to drive each way. Metro’s union rules require a five-minute break at the end of each cycle, and let’s suppose five minutes of padding per cycle are required to make the bus keep time reliably. The cycle time of this route is 27 + 27 + 5 + 5 = 64 minutes. Knowing this, we can work out that a pattern that maintains a clock-face schedule with 30-minute frequency would require three buses in service at once; 15-minute frequency would require five buses; and 10-minute frequency would require seven buses.
This simple example leads us to an important insight: routes that operate more frequently can almost always be scheduled more efficiently than less-frequent routes. In our example, going from 30-minute to 10-minute headways is a 300% increase in service that requires only a 233% increase in service hours; the difference is made up by shorter layover times. Of course, in some cases, route timing will line up just right so as to make the efficiency savings of increased frequency quite small; I chose the number 27 as a somewhat extreme example to make my point. Nonetheless, awkward route lengths occur quite frequently in the real world.
Knowing this, and looking at a map of current Queen Anne-Madrona service, we can see the problem:
Metro’s daytime service on this part of the network consists of one 15-minute route, plus four 30-minute headway routes that are interlined together to provide 15-minute headways in their most popular sections before wandering off into the neighborhoods. During the week, additional trips run from Virginia to 21st Ave, effectively creating a sixth route. Having all these different termini wastes a tremendous amount of driver and bus time; and this is where the restructured service is brilliant:
By splitting the 2S into a separate 15-minute headway route, and bringing all the other routes to a common terminus at the north, those routes can be scheduled as if they were a single route with sub-10-minute headways rather than four or five different 30-minute routes, leading to dramatic cost savings analogous to our simple example above.
These cost savings are enough to allow for the extension of frequent service out to Madrona* and into Sunday and evenings in East Queen Anne. This analysis also addresses the objection that this potential restructure over-serves the north side of Queen Anne. Certainly, nothing there justifies sub-10-minute service, but it is just a pleasant side-effect of the cost-saving one-terminus routing. Extending frequent service to Seattle Pacific, along with extending the 2X on Nickerson also allows some possibilities for improving Route 17; I will discuss this in a future post.
One objection this analysis does not address is that it might be better to maintain all-day service on Route 2N, extending the trolley route to the terminus of Route 13, splitting headways between
3rd 6th Ave W and Queen Anne Ave. To justify that change, we’ll have to examine the question of whether riders prefer higher frequencies versus wider geographical coverage, and I’ll examine that question in depth in future posts.
* There’s actually even more to it than that: additional service out to Madrona is almost free (versus an alternating turnback at 21st Ave providing 30-minute headways) because of how the cycle-time pencils out in either case. Reducing the south of the network to two terminals also saves money, just as reducing the north from four to one does, although the savings are not as dramatic.