There has been a lot of media coverage recently regarding the increasing prevalence of potholes on New Zealand’s road network. While potholes can be damaging as well as frustrating and annoying for drivers & cyclists, given the pressure on our roading budgets, should potholes be getting the prominent focus of engineering budgets?
Road surfacing condition has a serious effect on safety, as well as the quality of our travel experience. We all know what it feels like to travel along a smooth, new sealed road versus one that is deteriorating.
Research also shows that small deteriorations in the condition of the surface, can have a massive impact on crash risk – as much as 30%[1]. This can include potholes, but also surface rutting, corrugations and flushing, where it loses its chip surfacing, creating a shiny surface on the road that reduces tyre grip, which creates further risks[2].
But those aren’t the surface defects that are shared in the media, nor the defects that are so often the red-hot topic that has your neighbour shaking their fist and proclaiming road controlling authorities have no idea what they are doing. No. Potholes alone seem to get such a visceral hatred towards them. It’s almost as if the transport system succeeds or fails based on the number and size of potholes.
From a safety perspective however, how big is the pothole problem? Looking through New Zealand’s injury crash statistics over the last five years, the figure below shows the results for pothole related crashes.
Now, let’s address what all road safety engineers are thinking first. No death or serious injury is acceptable. I stand by that statement. While potholes make up less than 1% of recorded fatal crashes and just over 1% of serious injury crashes, these crashes are still unacceptable. Agreed. We do however need to consider that potholes are only one element that comes into consideration in these crashes. If a car hits a pothole and loses control, there are still several outcomes that can result.
If it is in a Safe System aligned rural environment, with safe and appropriate operating speeds and correct road safety infrastructure, the crash is unlikely to result in serious injury or death. On the other hand, if the road has a higher speed environment and road side hazards, such as trees or power poles in close proximity to the road with no protection, then things might not end so well.
If we consider New Zealand’s Safe System approach to road safety, creating a Safe System environment doesn’t claim to eliminate all crashes. Instead, a Safe System highlights that the priority should be ensuring crashes that do occur, don’t result in serious injury or fatality.
So what is the solution? Potholes do need to be addressed, since they increase the likelihood of crashes and create defects in the road, and if left unaddressed, will continue to worsen. Potholes can also increase costs on drivers, who may need to pay to get tyres, wheel alignment or suspension fixed. However, from a system perspective, we need to recognise that potholes are only a minor part of the problem and acknowledge there are much greater safety concerns that we should be pushing to prioritise, such as low friction, flushing unprotected roadsides and unsafe operating speeds.
So, the next time you see a pothole. Report it, but also look at the road environment’s safety features and consider what would the outcomes be if you were to crash right now. Is this road environment safe? And if it isn’t, maybe consider what is more dangerous – potholes that are factors in about 1% of DSI (Death & Serious Injury crashes) or lack of correct safety infrastructure and unsafe speeds which, combined, dictate the severity in every crash.
[1] https://www.nzta.govt.nz/assets/resources/skid-resistance-investigation-treatment-selection/docs/T10-skid-resistance-investigation-treatment-selection-201306.pdf
[2] https://www.nzta.govt.nz/resources/19-05-treatment-of-flush-and-bleeding-road-surfaces/#:~:text=Definition%20of%20flushing,results%20in%20minimal%20surface%20texture.
Lewis Martin
Principal Transportation Engineer