Capacity

This is a project exploring a discrete event simulation of transit systems.

It is designed to build a model of a transit system out of GTFS exports from transit agencies.

Latest Posts

• Stop Time Tracking

  Some months back, I started to compare the performance of the simulated schedule with the scheduled completion time of a run. The idea was that as soon as I could get that logging in place, I could start adding some random delays and measure the impact. However, I quickly noticed a deficiency in the existing model.

• Reverse Handlers Pt. 2

  Unsurprisingly, debugging reverse handlers is difficult. After many months of digging around, I’ve finally been able to work the reverse handlers, and their associated components into decent order. Below, I discuss a number of the unexpected challenges that made the process difficult.

• Reverse Handlers Pt. 1

  Over the past few weeks (months?), I’ve been working on the reverse handlers for the Transit Unit and Station state machines. Unsurprisingly, this turns out to be quite difficult. While writing a “draft” of the handlers isn’t too hard (i.e. figuring out what I think I want to do). Turning that into correct implementations has proven a little tricker than I expected.

• Building The Graph

  Next up, we’ll discuss the construction of the graph abstraction that forms the underlying structure for much of the simulation. Specifically, we’ll take a look at how to transform General Transit Feed Specification into something a little more useful for simulation, including some of the (probably dangerous) assumptions that were made along the way. It’s possible some of these assumptions include some idiosyncrasies of the LA Metro data, but my hope is that is largely not the case.

• The State Machine

  Here, we will explore the design of the LPs that will drive the majority of the experiment. The goal here, was to model it loosely after the airplane example given in the ROSS wiki. However, despite its clarity, that example is incomplete, so I had to do a bit of just-trying-it, which may have resulted in non-optimal use of the ROSS environment. In any event, let’s get into the details.

• Simulating Trains

  On the Internet, a lot of people have a lot of opinions on trains. Often, these result in discussions dominated by crayonistas making bold assertions about what is and isn’t possible and what is and isn’t a good idea.

  This raises a natural question: is there a quantitative way to measure what is a good idea, based on publicly available data?