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Safe speeds study claims savings, but are they imaginary?

In brief
  • A draft study of Auckland’s Safe Speeds programme claims Aucklanders save about $10M yearly. 
  • Benefits like public health improvements and journey time predictability are impossible to quantify.
  • Researchers admit small changes in methodology can have significant impacts on estimates.
  • Why do governments in NZ pay for these useless studies and why does NZ media not criticise the exercise?

What’s the point of this safe speeds study?

A study by BERL (Business and Economic Research Limited) on the economic benefits of Auckland Transport’s (AT) three-year-old Safe Speeds programme concludes the city is saving about $10M per year

Safe speeds study claims savings, but are they imaginary?
The connection between reductions in congestion and lower speed limits is not clear-cut.

But why was the BERL study commissioned in the first place, if, by AT’s admission, the conclusions are ballpark figures (we think that is a kind description), and  tiny adjustments in assumptions can make a big difference to the answer? 

Torturing facts to reach certain conclusions

For starters, this study is a draft  and, since it’s funded by a government that wanted to show a benefit, it’s not surprising it does.. 

The study values total benefits at $17.5M with a benefit-to-cost ratio of 2.5 to one. However, quantifying the value of benefits, such as the improvements in public health or the value attributed to predictably consistent journey times, is inherently a  guessing game, at best. BERL admits that minor methodological tweaks could lead to significantly divergent results from those initially presented (see below). 

The study does acknowledge the programme’s “disbenefits”, including less efficient vehicle operations and extended journey times valued at nearly $7M. Yet, like the conundrum in quantifying benefits, is there any hope  the ‘disbenefits’ can be accurately measured? 

Reduced congestion is valued at $5.1M – roughly half the total savings. In addition to this number also suffering from the same “impossible to measure” problem, a link between lower speed limits and a straightforward reduction in congestion is far from clear-cut.

There’s also the assertion slower speeds could make people feel safer, encouraging more people to walk or cycle – estimated to be worth around $3.5M annually. Longer journey times could become more predictable, which is estimated to be worth another roughly $3.1M. This is based on the idea that businesses benefit from greater certainty. But again, all these numbers are guesses.

Small changes make a big difference

The study also says slower speeds might cost the city around $2.1M a year. They arrived at this by calculating a reduction of 6.2 seconds per kilometre driven. Not surprisingly, BERL agrees these estimates are sensitive to even small changes.

For instance, the researchers say that adding just one second to the 4.5 seconds saved due to reduced congestion causes the benefits to jump by 18% – almost an extra $1M.

Similar analyses confirm the doubts

The formula to determine economic benefits from reduced speed is not something universally agreed upon. For example, one recent study from Canada’s Victoria Transport Policy Institute found that commuters often opted to save money over time. 

Challenges of bridging subjective judgement with objective analysis like the BERL study echoes a 2019 research paper by Ezra Hauser of the University of Toronto. 

The reality is that many variables are too subjective to be quantified and are really just reflections of the personal preferences of the study’s authors and sponsors. 

Do they expect the public to buy into this nonsense like the non-questioning media seems to?

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