When the seven roads of national significance were announced back in March this year I don’t think I quite appreciated the extent to which transport prioritisation would be based around them. However, one thing did stand out at the time – and that was how strange it was to include the link between Puhoi and Wellsford. I could have understood Puhoi to Warkworth at a stretch, but all the way to Wellsford? For those of you who don’t know, the road from Puhoi to Warkworth is pretty windy and hilly, but the road from Warkworth to Wellsford basically goes through a range of hills – through what’s called the “Dome Valley”. It’s a very windy stretch of road that does have a pretty poor safety record, but would be incredibly difficult to ever get something resembling a motorway alignment along it due to the hills.
So yeah, needless to say I was pretty surprised an upgrade of that road to something like motorway standard was considered one of the top seven transport priorities in the entire country. Since that time, we haven’t learned particularly much more about what is proposed for this road of national significance, other than it’s likely to cost around $2 billion and that $100 million has been set aside over the next three years in the National Land Transport Programme to conduct a detailed investigation into the route, to analyse its economic benefits and to undertake some land purchasing to secure a future designation for a realignment.
With a project like this, I imagine that most of its possible benefits would arise from “travel time savings”. Now it’s no secret that I am skeptical of travel time savings as the way to determine whether or not a project goes ahead (generally because studies show that improving the road networks encourage people to drive further and more often, rather than for them to have shorter trips). But anyway, I suppose that for now we’ll just have to accept that this is the way NZTA analyse projects. So what would the benefits of this $2 billion project be?
Now obviously I’m not NZTA and I don’t have a huge amount of complicated software and traffic modeling programmes to do this properly, but from what I’ve learned via the analysis of the Waterview Connection project, I think I have some idea about how things work. The Waterview Connection’s justification is largely on the basis of the motorway link providing $2.6 billion in time savings benefits – with this apparently being the result of 90,000 vehicles a day each saving around 15 minutes in travel time compared to the ‘do nothing’ option. NZTA basically assign a dollar value to each minute saved, then add it all up over the course of however many years are taken into account. Now this system is flawed in my opinion, due to questions over how it deals with induced demand, but for now let’s put that aside and apply the formula to the Puhoi-Wellsford link.
The existing road is about 37 kilometres long – between Puhoi in the south and Wellsford in the north. Warkworth is slightly on the Puhoi side of in the middle of the two routes. According to Wises Maps, the 37 km trip should take about 27 minutes. This is shown in the diagram below:
That’s an average speed of 83 kilometres per hour – to do the 37.7 km in 27 minutes. Not too unrealistic as the Puhoi to Wellsford stretch is typically quite gentle and easy to go 100 kph apart from a few nasty corners. The Warkworth-Wellsford stretch is slower from experience, and has an 80 kph speed limit along much of it these days too. But once you’re north of Wayby, the road is pretty straight all the way to Wellsford.
So, looking at alternative alignments, the map below shows a possible alternative that would shave about 6km off the length of the journey, and would also manage to miss the nasty hills of the Dome Valley. There is one area where the road might need to have a tunnel – to the south of Warkworth at the last mountain before it reaches the flatter land where the railway line (the black line) runs. So, assuming that this new alignment is motorway grade and you can do an average speed of 100 kph along it, it would take about 19 minutes to make the trip between Puhoi and Wellsford along this new route. So that’s an 8 minute time saving from the current route. To be generous, I’ll say a 10 minute time saving – just to make up for whether Wises have taken into account the 80 kph speed limit through Dome Valley (I think they’re a bit optimistic saying only 27 minutes from Puhoi-Wellsford).
Well a 10 minute time-savings is obviously not bad, although it is lower than the 15 minutes that the Waterview Connection will supposedly bring. The next part of analyzing the actual “time savings benefits” is to look at the number of vehicles that will use the road. Fortunately, that data is easily accessible on the NZTA website. I include detail of the relevant traffic counts below, showing counts at various points between Puhoi and Wellsford over the past five years, as well as averages for the whole route:
So generally there’s a vehicle count of around 15,000 vehicles-per-day along this stretch of road. Furthermore, over the past five years the flow hasn’t really gone anywhere – so it’s reasonable to suggest that levels are fairly stable and are unlikely to increase dramatically in the short to medium term future.
Now if we put all the pieces of this puzzle together we can come up with some fairly interesting results. I have worked out Puhoi-Wellsford’s time savings benefits by basically applying the same ratio of hours saved per day between the two projects to time savings benefits between the two projects (ie. Puhoi-Wellsford only provides 11% of the time savings as Waterview):
Now I’m sure there are other benefits that the road will bring, like safety benefits and congestion relief benefits (goodness knows how they’re different to time savings benefits, but they were counted separately by the Waterview Connection business case…) So perhaps these might add on another $100 million in benefits (I do feel like I’m being really generous here.)
In the end though, whatever way you look at it, $389 million of benefits is NOT worth $2 billion being spent on this link. That’s a cost benefit ratio of 0.19. Less than 20c of economic return for every dollar spent. Surely other projects make more sense than this?