Open modelling of the benefits of transport investment.

I’ve written before about the excellent open data on public transport timetables that’s available in the UK.

A few weeks later I wrote about one way that we can use that data; to create open transport accessibility maps and travel time matrixes.

In this blog post I’m going to follow up on a few paragraphs from my first blog post.

“Once you are in control of your data and your tools for analysing that data you can do even more. The effect of new roads or road closures, of new cycle paths, of new bus routes and tram lines can be modelled quickly. Business cases for investment can be made” I said. Here’s how we do that.

GTFS: the power of simplicity.

The starting point is the GTFS format that Google made the global standard for public transport data. This simple format is well-documented and easy to use so we can create new timetables for new services and add them to our transport planning models.

In the example below I create a rail service running from York to Leeds to Bradford to Manchester to Manchester Airport and then to Liverpool, taking a total of 55 minutes.

GTFS is a well-documented and simple format so it is easy to create imaginary timetables.

I let the train run every twenty minutes in each direction. That’s six trains running backwards and forwards all day, with a five minute changeover at each end.

The service is similar to the high speed trains that run today between London and Folkestone.

Accessibility from Bradford

We can calculate accessibility isochrones using real timetables supplemented by artificial ones in the same way as we calculate them using just real timetables.

Current accessibile population by public transport of Bradford in 1 hour, 2 hour, and 3 hours, and modelled accessibility with Northern Powerhouse Rail.

We see the large accessibility improvement that Bradford enjoys, at the centre of Northern Powerhouse rail and currently poorly served by public transport.

While maps capture much of the complexity of the changes in accessibility, they need extra work to be made simpler and more useful.

One way to do this is by calculating the population living within each isochrone. So we can calculate that the accessibility of Bradford by public transport within one hour increases from 1.2 million to 2.7 million, 130%, if Northern Powerhouse Rail is built.

We can project a population increase into an estimated economic benefit if we assume that large cities are more productive. I’ve done estimates of this in the past using data from France and the UK and I may estimate them for Bradford later. They are highly uncertain methods, but probably no worse than vastly more complicated alternatives.

Accessibility in detail

One of the biggest temptations I see when working with models like these and this kind of data is to add complexity to a problem. For example, we can calculate isochrones for accessibility for any number of minutes.

Detailed accessibility isochrones from Bradford in 15 minute increments if Northern Powerhouse Rail is built.

While this creates beautiful maps, it probably confuses us more than it adds value to our analysis.

Journey times are variable, returns on agglomeration are uncertain, and measuring changes in more detail is often just dabbling in these uncertainties.

The one hour and two hour isochrones and the accessible population increases of +130% to 2.7 million and +80% to 10.6 million are probably most of what matters.

Costs and models

This work is part of a long interest that I’ve had in reducing the amount of expertise and increasing the amount of politics that goes into UK transport investments. Not because I dislike experts, but because I think that their complex models are making investment decisions worse not better.

This work gives us a strong foundation for estimating the benefits side of a ratio, the Benefit Cost Ratio, that plays a small role in deciding whether the UK government will fund transport investments. And it works just as well for cycle lanes, bus lanes, and tram lines.

What we are missing is the cost side of the ratio. We need the C in the BCR.

Can you help? Do you have any good methods for estimating the cost of transport investments? Given the huge cost overruns of projects like HS2, Thameslink, and Crossrail as well as the underspends on projects like Greater Manchester’s Metrolink, I suspect that rules of thumb aren’t much worse than detailed estimates. But I don’t know.