The government has released its Road to Zero consultation document, laying out a Vision Zero approach aiming for “no one is killed or seriously injured in road crashes”.

A zero-road toll pledge may be a good soundbite, but not a good policy prescription.

While we all want safer roads, an inconvenient truth is that not all crashes are preventable and, sadly, sometimes human mistakes do cost lives.

Until autonomous driving frees us from human errors, misjudgments and infringements, the only certain way to prevent deadly crashes is to ban driving altogether – which, of course, is absurd.

So extending an olive branch to reality, Road to Zero proposes a 40 percent reduction in deaths and serious injuries by 2030, as “zero deaths and serious injuries on our roads may not be achievable in the next ten to 20 years”.

That is a more sensible and achievable goal worth pursuing.

Unfortunately, the document does not formalise a way to compute the inevitable trade-offs between road safety, policy action alternatives, and mobility costs.

As it stands, to reach the 2030 target under Vision Zero, anything goes no matter the relative costs – or more importantly, who bears the cost.

That means New Zealanders inadvertently might be signing up for massive speed limit downgrades, a booming infringement ticket industry, and expensive car safety upgrades.

When government data released last month showed nine out of 10 open roads have speed limits above the recommended, there were prompt calls to reduce top speeds across the board.

Never mind in many cases, a cost-effective alternative would be much-needed improvements in the quality of road infrastructure. (Switzerland, for instance, has a third of deadly crashes per capita than New Zealand, while maintaining 120 km/h speed limits on its motorways.)

But a chain is only strong as its weakest link. It is one thing to have grand Vision Zero goals, another to commit public resources to fund them.

Under the proposed framework, in any policy combination involving, say, infrastructure upgrades and lower speed limits, the latter is likely to prevail – with lots of speed cameras to enforce it as well.

To avoid this scenario, let us hope the government’s final decision on the road safety strategy conducts proper cost-benefit analyses when weighing the pros and cons of each policy option – including the costs and benefits of safe, timely and reliable road mobility.