Higher speeds lower productivity: what the data shows crash delays really cost Auckland

Another morning, another crash on one of Auckland’s major roads. Traffic isn’t moving. Drivers sit in their cars rehearsing reasons for being late again. Radio hosts offer the usual advice: leave earlier and find an alternative route.

It happens so often we barely notice anymore. But the costs add up fast, and they’re far bigger than a few delayed meetings.

Auckland had 34,628 reported crashes between 2022 and 2025. The “road toll” conversation typically stops at the obvious costs: injuries, deaths, emergency response. But it misses a lot.

A new analysis puts the true figure at NZ$9.23 billion over those three years (roughly 2% of Auckland’s $157 billion economy), including nearly $200 million that never enters the policy debate.

Transport agencies already put dollar figures on crashes. The New Zealand Transport Authority (NZTA) uses official methodology covering the usual: medical bills, lost productivity, property damage and the statistical value of a life. One fatal crash amounts to $15.2 million.

But buried in the technical reports is an additional cost category that most policy discussions ignore: network disruption.

False economies

Crashes on major roads hit more than just the people involved. Thousands of other drivers get caught in the delays that spread across the network.

Traffic engineering consultancy Flow Transportation Specialists recently worked out these network delay costs for Auckland Transport for the first time.

Using GPS travel time data and traffic counts, researchers tracked how crashes create congestion that extends far beyond the crash scene and persists long after vehicles are cleared.

A multi-vehicle crash on Auckland’s motorway network generates between $1.4 million and $3.5 million in network delay costs. Even a serious crash on an arterial road can cost $26,000 to $37,000 in lost time across all affected road users.

When applied across Auckland’s crash data, network delays add roughly $195 million to the region’s crash costs, a 2.2% increase over conventional estimates.

These costs matter to the debate over the current government’s rollback of its predecessor’s speed reductions. The claim is that moving traffic faster will boost productivity and grow the economy.

But there’s a problem with this logic. It counts time saved from higher speeds as pure economic gain, while ignoring the time lost when those higher speeds increase crash frequency and severity.

Drop speeds from 50 kilometres per hour (km/h) to 30km/h and pedestrian deaths in crashes fall from 80% to 10%. Faster speeds involve less time to react and longer stopping distances, meaning more crashes.

And higher speeds mean worse crashes that take longer to clear. A fatal crash can shut a road for hours. At 110km/h, there is more debris, longer investigations and longer queues compared with the same crash at 100km/h.

Productivity isn’t about speed

Transport agencies worldwide, including the NZTA, follow a “safe system” approach to road safety. The argument is that humans make mistakes, and road design should stop those mistakes from becoming deadly. Speed management sits at its core.

Rolling back speed limits moves New Zealand outside this evidence-based framework. It prioritises theoretical time savings over documented safety benefits, creating a false economy where minutes or even seconds saved in normal traffic come at the cost of hours lost, and billions spent, when crashes inevitably occur.

The crash cost estimates come with a few caveats. Flow Transportation Specialists developed their analysis with just four case-study crashes. Minor crash costs on major roads are extrapolated guesses rather than measured data.

And the methodology doesn’t account for vehicle operating costs during delays, cancelled trips, schedule reliability impacts and emergency vehicle delays. The true network delay figure is probably higher.

But even these conservative numbers run to hundreds of millions, costs that don’t show up when agencies decide which projects get funded. Underestimate crash costs by 3–10% and safety upgrades start losing cost-benefit battles they should win.

Crashes and consequent delays slow cities more than speed limits do. Productivity comes from fewer crashes and predictable journeys, not from letting people drive faster until something goes wrong.

Next time you’re sitting in traffic behind a crash, consider the actual bill: emergency response, medical costs, lost work hours, property damage. Now add the network delay costs hitting thousands of other drivers.

Rolling back speed limits means choosing to ignore those hidden costs.

Timothy Welch does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.