Network Approach to Setting Speed Limits

NEW ZEALAND TRANSPORT AGENCY 

ISSUE STRATEGIES TAKEAWAYS

➤ Speed limits can be inconsistent

➤ In some cases, speed limits did not

consider the safety aspect of speed

➤ Developed network based speed

limits that were evidence based

and nationally consistent

➤ Used outreach and education

➤ Used a measure of safety risk

which can be communicated to

stakeholders and the public

➤ Data-driven approach provides

clarity in selecting speed limits

Background

Speeding is a contributing factor in almost one-third of 

fatalities and around 20 percent of serious injury crashes in 

New Zealand1,2. Additionally, roadway fatalities increased from 

253 in 2013 to 373 in 2018 while serious injuries increased 

from 2,020 to 2,8363. 

The Problem

Historically speed limits in New Zealand were based on the 

number of access points and surrounding land use for a 

particular rather than considering roadway characteristics or 

safety performance. 

Developing Consistent and 

Evidence Based Speed Limits

To address concerns about speeding-related crashes, the 

New Zealand Transport agency developed the NZ Speed 

Management Guide which provides speed limits that are 

nationally consistent and evidence based2,4,

. The resulting 

guide is an evidence-based, network-wide approach that 

recommends speed limits that are safe and appropriate based 

on road function, design, safety, and land use. 

The objectives of the guide are the following5:

• Make the roadway system more forgiving of human error

• Reduce force in crashes to a level that is tolerable for the

human body to survive without serious injury

• Minimize unsafe road user behavior

A recommended speed limit for each roadway type is 

developed based on various characteristics such as geometry, 

land use, roadside hazards, etc. An Infrastructure Risk Rate 

(IRR) is developed for each corridor based on the following 

and an IRR score is given (1 = low to 5 = high risk): 

• Roadway type

• Alignment

• Width

• Roadside hazards

• Land use

• Intersection density

• Access density

• Traffic volume

Speeding contributes to 1/3 of 

fatalities in New Zealand and is noted 

as being on par with drunk driving as 

their biggest safety problem2.

Speeding Vehicle. Source: Getty Images

Case Study 8: Noteworthy Speed Management Practices 1 FHWA-SA-20-084
Network Approach to Setting Speed Limits

A measure of safety risk (low-to-high) is also assigned 

based on crash density and crash rate6. The IRR score is 

combined with safety risk and roadway function and a safe 

and appropriate speed recommended. The guide lays out 

principles for setting speed limits and applying speed 

management measures to ensure they are consistent across 

similar roadway types in a network4. A matrix was developed 

which recommends safe and appropriate speeds for a 

particular road class. An example of recommended speeds for 

a few roadway types is shown in Table 1.

Table 1: Example of Recommended Speeds for Select Road Types

Roadway Function Road Safety Metric Infrastructure Risk Rating

Safe and 

Appropriate 

Speed

➤ ONRC* Class 1 -2

➤ Rural town

➤ Personal risk ≤ low to medium**

➤ Collective risk ≤ medium to high**

➤ Low or Low-medium 80 km/h

➤ ONRC* Class 1 - 3

➤ Rural town

➤ Personal risk ≤ medium** ➤ Low or Low-medium 60 km/h

➤ Any ONRC*

➤ Rural town

➤ Personal risk ≤ medium to high** ➤ Low or Low-medium 50 km/h

*One Network Road Classification **Risk is further defined in the NZ Speed Management Guide

Typical rural road in New Zealand. Source: Getty Images

Case Study 8: Noteworthy Speed Management Practices 2 FHWA-SA-20-084
Network Approach to Setting Speed Limits

The New Zealand Transport agency develops a map for each 

Road Controlling Agency, which shows where existing speed 

limits differ from the recommendations, and identifies where 

speed management will have the most benefit. Maps are 

developed using land use, speed limits, current operating 

speeds, and a measure of risk for the corridor4.

The network map is created by comparing existing speed limits 

against the recommended ones. Corridors with a safety issue 

and current travel speeds and speed limit above the calculated 

safe and appropriate speed are identified. The next step is to 

determine what type of intervention should be done for those 

corridors. Economically important roads where there is a strong 

case for investment are targeted for geometric improvements 

such as by-passes. When corridors do not meet these criteria, 

discussions are made about lowering the speed limit or 

employing lower-cost countermeasures. Finally, in locations 

where current travel speeds are below the current speed limit, 

lowering the speed limit is recommended to be consistent4. 

What Happened Next

The speed management guide was used to develop a tool 

called “Mega Maps” which assigns speeds within a particular 

network area based on factors from the NZ Speed Management 

Guide2. Application of the tool for fatal road crashes in 2018 

found 61 percent of fatal crash sites had a calculated “safe and 

appropriate speed” that was below the currently posted speed 

limit at that site2. This information allows agencies to better 

target speed limits for high-risk roadways.

New Zealand has also announced a $1.4 billion investment 

in road safety over the next 3 years with half of the funds 

allocated to state highways and half allocated for local roads. 

Improvements include the use of median and side barriers, 

rumble strips, and should widening3.

In Auckland, around 750 km of roads are being treated. The 

focus is on the top 10 percent high risk areas5.

Key Takeaways and Lessons Learned

Data-driven approach – New Zealand used a data-driven 

approach that can be replicated by other agencies. Speed 

limits were assigned based on an assessment of roadway 

characteristics (i.e., width, volume, and alignment) as well as 

crash density and rate. A measure of safety risk is assigned. 

In addition to having a clear metric for assigning speed limits, 

the concept of risk can be explained to agencies and the 

public more easily. 

Outreach – As NZ began implementing the guide and tool 

they found some resistance. For instance, the use of the 

guide and tool resulted in speed limits on a large number of 

roadways being classified as “too high.” One source reported 

that 87 percent of speed limits in New Zealand are too high 

according to the tool with only 5 percent of open roads 

warranting the current 100 km/h speed limit. Others expressed 

concerns that blanket reductions could weaken the economy 

by increasing time for businesses to move freight7.

To address these concerns, New Zealand found engagement and 

outreach were an important part of the process. Their approach 

and perspective for implementation included the following: 

• Focus on “speed management” rather than speed limits

• Engage early with stakeholders

• Gradually build public understanding and support

• Consider the pace of change, resistance occurs when too

many things are changed at once

61 percent of fatal crashes were 

found to occur on roadways where 

the calculated “safe and appropriate 

speed” was below the currently 

posted speed limit.

1 Safer Journeys. Safe Speed: Goal for 2020. www.saferjourneys.govt.nz/action-plans/safe-speeds. Accessed November 2019.

2 Koorey, Glen. Making Safer Speeds Happen. Can Do Workshop. July 2018 https://can.org.nz/system/files/GKoorey-CANDo-2018-LowerSpeeds.pdf

3 Tupou, Laura. “Government Announces a $1.4 Billion Investment in Road Safety.”

www.newshub.co.nz/home/politics/2018/12/government-announces-1-4-billion-investment-in-road-safety.html. December 16, 2018. Accessed November 2019.

4 New Zealand Transport Agency. NZ Speed Management Guide. November 2016. www.nzta.govt.nz/safety/speed-management-resources (Accessed October 

2019).

5 Turner, Shane. Applying the Speed Management Guide to New Zealand Cities.

Presentation at the 2020 Annual Meeting of the Transportation Research Board. Washington, DC. January 2020.

6 KiwiRAP. KiwiRAP, New Zealand Road Assessment Programme. www.kiwirap.org.nz/index.html. Accessed November 2019.

7 Ensor, Jamie. Speed Limits Too High on Nearly All Kiwi Roads. New Zealand Transport Agency 

https://www.newshub.co.nz/home/new-zealand/2019/06/speed-limits-too-high-on-nearly-all-kiwi-roads-nzta.html.

Case Study 8: Noteworthy Speed Management Practices 3 FHWA-SA-20-084