Vision Zero for engineers

A safe system is well engineered, maintained and operated

The responsibility of the road engineering sector is to help take New Zealand toward Vision Zero, a New Zealand where no one is killed or seriously injured on our roads.  

The sector will do this by designing, maintaining and operating a forgiving road network that takes human fallibility and vulnerability into account. Under a Safe System we design the whole transport system to protect people from death and serious injury.  

We will do this by embedding the Safe System principles in our policies, guidance, standards and processes. This ensures the way we design, operate and maintain our transport network not only reduces the chance of a crash occurring but also reduces the severity of that crash when it does occur.

What role can engineers play?

Vision Zero for engineers means implementing and maintaining “Primary Safe System” infrastructure and speed measures wherever possible, i.e. median barriers, speed management, roundabouts, raised safety platforms. It’s acknowledged it may not always be possible to implement a Primary Safe System intervention, however if a primary treatment cannot be achieved then there should be strong justification to support this. 

This is a change, as traditionally we’ve taken an incremental, risk-based approach in determining the most appropriate type of intervention. And those interventions were not always Safe System aligned and generally led to limited, or even poor, safety outcomes (ie high-volume roads without median barriers, high volume high speed signalised intersections, at-grade/non separated pedestrian crossings and cycle facilities). 

The Safe System is the gold standard in road safety and underpins Road to Zero

The Safe System principles are:  

  • We promote good choices but plan for mistakes.
  • We design for human vulnerability.
  • We strengthen all parts of the road transport system.
  • We have a shared responsibility. 

Examples of how engineers can apply Safe System principles

The Safe System principles can be applied in road and street design, maintenance and operations. In engineering terms, it is about understanding and managing crash forces to within survivable limits. 

The Safe System approach means a change in mindset

Issue Traditional approach Safe System approach

Some deaths are inevitable   

As long as we were making a good go at improving things, people accepted that some road deaths would still occur, and would be satisfied with some improvement.  

Road deaths are preventable  

We know road deaths are preventable. It’s not acceptable to accept the status quo. By taking a system approach, and choosing Safe System interventions, we can drastically reduce the level of harm on our roads.  

Human error 

Expect perfect human behaviour  

Human error was often seen as the excuse for inaction, and effort was focused toward improving driver behaviour rather than infrastructure.  

Plan and design for mistakes, people are fallible and vulnerable   

A ‘forgiving’ transport network is core to the Safe System. Death and serious injury crashes should not occur as a result of driver error. Vehicle and infrastructure/speed improvements should be used to reduce impact forces (should a crash occur) to within human biomechanical tolerances, and therefore reduce the harm.  

Responsibility   Blame the road user   

The focus was on driver education to address road user error which consequently lowered the responsibility of system designers.

System designers are also responsible for creating a Safe System

System designers share the responsibility for safe travel outcomes by accommodating people errors.  

Crash severity addressed  

Total number of crashes  

Total crashes (of all severities) was often used to identify problem sites. 

Crashes resulting in death or serious injury

Death and serious injury crashes and/or high-risk crash types should be the starting point in site identification. Minor injury and non-injury crashes may be useful to provide additional information but are not the core focus.  

Understanding speed at which deaths and serious injuries (DSI) occur for different crash types  

Biomechanical tolerances known but not core to decision making  

Information on biomechanical tolerances was available but was not core to the understanding of how to address risk.  

Biomechanical tolerances core to decision making to eliminate DSI  

Biomechanical tolerances are core to the vision of eliminating death and serious injury crashes.  

We need to understand and be guided by the speed at which DSI occur for different crash types.  

Design requirements   

High Benefit Cost Ratios (BCRs) chosen not eliminating death and serious injury

Treatment types were often selected based on high BCRs rather than eliminating death and serious injury.  

Must focus on eliminating death and serious injury  

It is paramount that new infrastructure assists in eliminating death and serious injuries. This also includes speed management and prioritisation/separation of different transport users travelling in different directions or modes.  

Safe System principles in design  

 The road system needs to be managed and designed in such a way that impact energy on the human body is:  

  • Firstly avoided - this includes considering the ways in which people respond to road conditions and design roads to minimise opportunities for error.
  • Secondly managed at tolerable levels, in the event a crash occurs - design a system that is error tolerant – ie design that is resilient to human error and will minimise harm when something goes wrong.  

For the Safe System approach to be fully embedded into New Zealand we need systematic application of these principles in road design, operations and maintenance.  

To translate the Safe System approach into application, the following questions should guide us: 

  • Is it possible to have a head-on crash at a speed greater than 70 km/h? 
  • Is it possible to have an intersection (right-angle) crash at a speed greater than 50 km/h? 
  • Is it possible to have a run-off-road (side impact with a rigid object) crash at a speed greater than 40 km/h? 
  • Is it possible to have a vulnerable person (e.g. pedestrian, cyclist and motorcyclist) crash at a speed greater than 30 km/h?  

Through implementing the Safe System approach there will be potential reductions of human error and, preventing crashes occurring, the priority is reducing the level of harm (death and serious injuries) when crashes do occur. 

Infrastructure and speed management improvement projects and programmes should address high severity, head-on, run-off-road, intersection (side impact) and vulnerable road user casualties where the appropriate value for money can be achieved.

Below is a list of guides and recommended treatments that will apply (and have benefits) across the whole system: 

High-risk rural roads

  • Shift focus from targeting isolated blackspots to addressing high-risk corridors to reduce the incidence and outcomes of crashes (in particular run-off-road and head-on). 

  • Identify high-risk road sections based on the actual or predicted high-severity crash density (crashes/km) and crash rate (crashes/vkt). 

  • Determine the appropriate level of treatment which may vary from higher cost primary Safe System interventions like median barriers and roundabouts to lower cost supporting Safe System interventions such as wide centreline, delineation improvements (including rumble strips), skid resistance and speed management. 

  • Prioritise the use of flexible, energy absorbing, cost effective barrier systems to provide forgiving roadsides.

  • Consider the opportunities for intelligent transport systems such as electronic warning signs and electronic speed management. 

For more information see our high-risk rural roads guide

High-risk intersections

  • Identify high-risk sites based on either their high-severity crash history and/or crash types such as crossing or turning movements.

  • Avoid creating complex driver decisions, minimise the number of conflict points and conflict angles, and keep potential collision areas free of hazardous roadside furniture. 

  • Look to challenge some of the more traditional intersection forms particularly in high-volume and high-speed situations, and how right turn and cross movements and traffic speeds are better managed. 

  • Consider how people walking or cycling are catered for at all intersections – remembering that lower speeds can reduce severity. 

  • When designing roundabouts which are one of the safest forms of intersection, people walking or cycling or using active modes, need to be considered too. 

  • Pay particular regard to visibility issues for all people. 

For more information see our high-risk intersection guide