Rapid transit – some observations about mode choice decision making

This article first appeared on TraNZport and is republished with permission.

The road to the mode…

There are two distinct problems that crop up every time I talk to someone about rapid transit, and they are both related to mode choice.

First, people tend to look at the situation of mode from too high a level. An example might be someone looking at the general characteristics of a city, and declare it is unsuitable for “insert mode here“. This could be on the basis of total population, population density, geography, or otherwise.

The second is that people tend to race to a specific mode to solve a problem. This is what I term the “killing two birds with one stone” approach, where a mode is seen as perfect for a particular route because it embodies several different aspects that solve more than one problem. This could be serving two different routes by the same mode rather than different modes, or, if you will, a third “compromise” mode.  It sounds good on paper, but the devil is always in the detail.

Defining what mode to use requires a more refined analysis

Let’s look at the first problem, which is distinctly macro. The problem with taking a view that a city shouldn’t invest in particular modes due to its general characteristics is that the economics of such decisions is far more nuanced. We have a pretty good example of that here in New Zealand with Wellington’s commuter rail network. For a city of not even half a million, Wellington’s rail network is both quite extensive and intensive. It works for its situation. And that is the point I would make.

Choice of mode should always be made in regard to the specifics of the situation. That means looking at the specific characteristics of the area the route operates, how the route fits into the wider network, and should also include the now, the planned and likely, and the could and preferred.

density nz
Christchurch is a low density city compared to Auckland and Wellington. Does that mean some (or all) rapid transit modes are not suited, regardless of the route specifics, future directions etc?

For example, the relatively low-density and low-populated Australian cities of Canberra and Newcastle have just introduced light rail (or will in April in the case of Canberra). That isn’t to say that the likes of Wellington and Christchurch should be introducing light rail, it just illustrates that general urban form on its own isn’t a good determinant of mode (or even the need for rapid transit in general). There is far more to it than that.

Choice of mode should be specific to a problem

At the other end of the spectrum, you have people who approach the issue from a “let’s go with mode X” perspective because it seemingly solves a lot of problems with one solution, or there is a push to maintain unbroken trips over transferring, or there are perceived significant benefits to operating as few modes as possible. Basically, the mode sounds good because it solves several problems in one hit.

An example might be building a busway over using adjacent railway lines because “buses are flexible and all routes can use the busway” or perhaps calls for tram-trains to operate Wellington’s commuter rail network so services can connect with a new light rail route in the city and southern suburbs, giving more “one trip” travel options (for an outline of the tram-trains and their particular application in Wellington, check out this article).

However,  I do think the push to maintain a single mode often overstates the benefits without mentioning the negatives. You can end up in situations  For example, it can put parameters on certain parts of the network that are dictated by the operating needs of others. This is a problem if different parts of the network a trying to do different jobs.

For instance, in the Wellington tram-train example, you would be trying to knit together a very all-day style rapid transit route over a relatively short distance along a quite dense corridor, with a peak-hour focused long-distance commuter service servicing primarily low density regional centres. It shouldn’t be too difficult to see the potential constraints a compromise, generic, solution might place on either section from doing the job they need to do. It could impact on capacity, frequency, and result in mixed operating patterns that negate the assumed benefits.

tram train
A Karlsruhe tram-train. Solving two problems in one? Good? Bad? Right? Wrong? Depends on the situation!

That doesn’t mean that some modes are bad, they can all work in certain situations where they work best, it’s just a reminder that there, generally speaking, is no perfect mode from a network perspective, and there a a lot of considerations that need to be made before mode choice is finalised.

So why is this important?

The reason I am discussing all of this is that it is important to be aware that:

  • modes should not be ruled in or out on the basis of a high level analysis of a an entire city and its general urban form used to dictate what is in or out
  • mode choice should be what is best for that particular situation (and that includes wider interactions with the rest of the transport network).

Sometimes the solution that advocates want isn’t necessarily the one that is going to get the outcomes they desire, or at least not at an early stage. On the other hand, it also means that you can’t just automatically rule anything out based on high level analysis of a city.

Finally, I’d like to point out something that is used quite a bit to drive the mode debate, in a New Zealand context, and that is transfers. There seems to be a focus on avoiding transfers in New Zealand when talking rapid transit. For example, the “station is too far from where people need to go” argument. This is a perfectly legitimate concern, but doesn’t mean that a transfer to a reliable, high quality service using another mode won’t stop it from being effective. Yes, we shouldn’t introduce transfers for the sake of it, but we can also impact on the quality of the overall network if we focus overwhelmingly on avoiding them (as set out above in my Wellington example). Transfers should always be a concern, but we shouldn’t compromise too far if it places limitations on performance. I’ll cover this a bit more later when…

Staging rapid transit projects

In a future post, I want to evolve this discussion to talk about how staging of projects is important, and how this can impact the way a proposal is presented to the public. This is my third problem with mode, but is far more detailed than the above two, so I will do a separate post on that soon.

One more thing…

For what it is worth, this is just my personal observation and opinion. Choice of mode brings forward strong emotions in people, for some reason, at times myself included I must say, so I must reiterate that I am not advocating for or against a particular mode, it is the method of mode decision making that I am particularly  interested in. I am someone who comes from a policy background, so understanding and defining the problem and evaluating solutions from multiple perspectives is in my blood, I’m afraid (yeah, I’m great company!).

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