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Transportist: April 2022
Sydneysiders will get 12 days of free travel across the public transport network after “the NSW Rail, Tram and Bus Union threatened to strike every Friday in June unless the government instituted a period of free travel for commuters as an apology for last month's fiasco when trains shut down for 24 hours.” This occurs during the school holidays when demand is lower.
We need a way of assessing strategic (i.e. UTPS-like ‘four-step’) transport models.
My first real job was working as a transport modeler for the Montgomery County, Maryland Planning Department. At the time, models were about a third of a century old, dating from the mid-1950s, deriving from the work of Douglas Carroll et al. in Detroit and then Chicago. I worked on developing a new model for the Washington DC region, (as we didn’t really trust the model from MWCOG, and wanted our own), Travel/2, using then current data and ideas in transport modeling. It had some good features which are yet to be mainstream like ensuring travel time consistency between trip distribution and route assignment, and used then au courant logit mode choice models and detailed trip generation. It wasn’t an agent (activity)-based model, the world wasn’t quite ready, TranSims was just being developed, though we played with the idea some and I wrote not very efficient Fortran code for population synthesis. Route assignment was still static (though multi-class), DTA was not an off-the-shelf product. We tried to document everything, (which is probably sitting in WordPerfect files on my computer) though there was no internet or GitHub to host our code or macros, and of course the source code for the modeling platform (EMME/2) was and remains proprietary, not open access.
Models have not advanced as much in the past third of a century since I started as we would have hoped at the time. Certainly they have moved in the direction we anticipated, just very slowly. Ideally we would assess their accuracy, there is some literature on ex-post analysis of course, and we have done that, but that takes too long, years are required to know whether the forecast was accurate, and by then decisions have been made and the models have evolved, so anything that was wrong was obviously obsolete and cannot be used to criticise the new models.
It should however be possible to assess the models (and each component model) themselves on a number of criteria, e.g. (but not limited to):
Methodological Quality (without prescribing a particular modeling technique, but definitely proscribing those that are known inferior),
Internal Consistency (the input travel times to travel demand equal the outputs from route choice, e.g.),
Calibration and Validity (how does the base model compare with observed data of various kinds, has backcasting been done, are the results accurate, … is this done systematically, following standard documented procedures?),
Recency of Estimation Data,
And develop some kind of scorecard that individuals or teams can apply to strategic transport models, roughly similar to how the ITDP BRT scorecard works. The score should not be a weighted average, but a product of the scores of the components. A zero on any attribute would result in a 0 for the whole thing. Models could then be rated as Gold, Silver, Bronze, or Tin. This can be used to argue for model improvements by external comparison in some sort of systematic (rather than ad hoc) way, perhaps using league tables to compare models, as well as providing a means to discredit bad forecasts, which is what scares away modellers from this approach.
The Zephyr Foundation aims to improve transport modeling, but it is largely organised by modelers themselves, and thus subject to political sensitivities.
Similarly, we need a way of assessing Business Cases (Benefit-Cost Analyses) (BCA) based on how good the methodology is.
Obviously many BCA in Australia often fail on the criteria of transparency and replicability, as they are tightly held as “Cabinet in Confidence” or “Commercial in Confidence”, so no one knows how the results were actually established. By the product rule, if they fail on that criteria, they fail on everything else, as none of the other criteria can be properly evaluated.
We can ask for some of the same kind of criteria as above. There are various industry committees (TRB, ATAP) that aim to improve and standardise methods, but I am not aware of anyone from outside the sector who is actually scoring the quality of the evaluation. Let me know of any.
Lahoorpoor, Bahman, and David Levinson. 2022. “In Search of Lost Trams: Comparing 1925 and 2020 Transit Isochrones in Sydney.” Findings, March. https://doi.org/10.32866/001c.33040. Has Sydney lost access by removing its extensive tram network? We compare the 1925 tram network with today’s bus network, and conclude that the access provided today exceeds what would have been provided by just trams. The Sydney CBD would have had better access if 1925’s central tram lines were still in operation.
Access by Trams and Trains in Sydney and Melbourne in the 1920s. Sydney map by Bahman Lahoorpoor inspired by map of Melbourne
[Cam Booth sells a restored version of the Melbourne map, suitable for framing]
The latter image is on the Cover of Elements of Access,
Research by Others
News and Opinion
A Play in Four Acts:
Western Sydney Airport Metro: fears $11b project won’t be ready, won’t return investment “highlighting the government’s own cost-benefit analysis reveals just 18 cents will be made for every dollar spent on the $11 billion project.”
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