Mednotes

L3 Public Health Road traffic injury prevention

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aliasesL3 Public Health Road traffic injury prevention

14 min read

Overview

This lecture uses road traffic injury as a case study for the public health approach to injury prevention. It covers how doctors contribute to road safety (regulation, advocacy, research), how injury is defined and classified, the global and Aotearoa New Zealand burden of road traffic injury, the WHO Decade of Action and Safe System approach, the history of NZ road safety legislation, and a detailed case study of evidence-based policy development for young drivers (Graduated Driver Licensing), closing with the Road to Zero strategy and recent policy debate over speed limits.

What doctors do to improve road safety

  • Regulatory: doctors contribute via fitness-to-drive assessment, illustrated by the “Medical Aspects of Fitness to Drive” guide for health practitioners (Waka Kotahi/NZ Government).
  • Advocacy: the Royal Australasian College of Surgeons (RACS) Road Trauma Committee has lobbied since 1969 for seat-belt laws, drink-driving countermeasures and helmet laws, with more recent focus on quad bike safety, personal mobility devices (PMDs) and alcohol-related trauma. NZ had 341 road fatalities in 2023 (down from 372 in 2022); 19 deaths over the 2023/24 Christmas-New Year period (vs 21 the prior year). RACS also submitted to the Australian Joint Select Committee on Road Safety (2021), endorsing the WHO/UN Global Plan Decade of Action for Road Safety 2021-2030 (target ≥50% reduction in road deaths/injuries); it noted ~100 people hospitalised daily in Australia from road crashes and ~$30 AUD billion spent annually managing this “silent epidemic.”
  • Research: a NZ case-control study (Connor, Norton, Ameratunga, Jackson; Auckland, April 1998-July 1999; 571 car driver cases involved in crashes with at least one hospitalised/killed occupant vs 588 controls) found blood alcohol concentration above 100 mg/100 mL increases crash-involvement risk 13-18x and fatal-crash risk 50-90x, with some increased risk below this level. Alcohol impairment is considered the most important contributing cause of car crash injuries.

Public health framework

A cyclical process for approaching injury prevention: Defining and measuring the problem → Describing causes and consequences → Developing and evaluating interventions → Disseminating effective policy and practice → Research and evaluation → loops back to defining and measuring the problem.

Defining and classifying injury

  • ICD definition: injury means physical or physiological bodily harm resulting from interaction of the body with energy (mechanical, thermal, electrical, chemical or radiant) or due to extreme pressure. Injury usually has rapid onset in response to a well-defined event (e.g. a car crash, striking the ground after a fall, drinking a strongly alkaline liquid) — these events are the “external causes” of injury. Injury includes manifestations evident immediately after onset (which may or may not persist) and manifestations that only become evident at a later date.
  • Coding an injury has two parts: what’s wrong (same as for chronic disease, e.g. “fracture of base of neck of femur”) and how it happened, i.e. the external cause (e.g. slipping, tripping, stumbling, falls).
  • Epidemiological triad: injury (like disease) results from interacting host factors, agent factors and environment factors, each influencing the others.

Global burden of injury

  • Worldwide causes of injury death (2012, WHO): road traffic injuries 24%, other unintentional injuries 18%, suicide 16%, falls 14%, homicide 10%, drowning 7%, fire-related burns 5%, poisonings 4%, war 2%.
  • By age group (2012, world), road traffic injuries are the number 1 cause of death for ages 15-29 (325,736 deaths), and rank in the top 5 for ages 5-14 (4th) and 30-49 (3rd) — injury is a leading killer specifically of youth and young adults, unlike the older age bands where cardiovascular and respiratory disease dominate.
  • Injury pyramid: demand on the health sector from injury forms a pyramid with fatal injuries at the top, then hospitalisations, then emergency department visits, then primary care visits, with the widest base being injuries treated outside the health system, not treated, or not reported. Costs and disability accumulate across all levels of the pyramid, not just at the fatal-injury tip.
  • WHO global road traffic fatality rates declined 2010-2021: from ~18 to ~15 per 100,000 population, and from ~80 to ~55-60 per 100,000 vehicles.
  • Low-income and lower-middle-income countries have markedly higher fatality rates per population than high-income countries (e.g. South-East Asia low-income ~42 per 100,000, versus much lower in high-income regions), by WHO region and country income level (2021).
  • The WHO/UN Global Plan, Decade of Action for Road Safety 2021-2030, rejects “business as usual,” calls for an integrated Safe System approach, and sets a target of 50% reduction in road traffic deaths and serious injuries by 2030.
  • Safe System approach: six interlinked domains — multimodal transport and land-use planning; safe road infrastructure; safe vehicles; safe road use; post-crash response; and system management — underpinned by principles including strengthening all parts of the transport system, planning to fail safely, designing for human vulnerability, making safety a critical decision-making priority, shared responsibility for road safety, and grounding actions in evidence.
  • WHO best-practice legislative criteria (five key risk factors): speeding (national law, urban limits ≤50 km/h, local authorities can further lower this); drink driving (national law defining BAC limits, ≤0.05 g/dL for the general driving population and ≤0.02 g/dL for novice drivers); motorcycle helmet use (national law covering all riders, road types and engine types, helmet must be fastened and meet a standard); seat-belt use (national law applying to all seating positions); child restraint use (national law requiring a child restraint system meeting a standard for children up to age 10 years or 135 cm height, plus prohibiting children below a given age/height from sitting in the front seat).

Aotearoa New Zealand epidemiology

  • Injury-related health loss (DALYs, 2006) by age and sex: in males, transport injury and self-inflicted injury both peak sharply around ages 15-24 (transport injury DALY rate roughly 20-25 per 1000), then decline, with falls rising steeply from around age 70+. In females, injury rates are much lower overall, with a smaller peak around ages 15-19 and falls rising sharply from around age 75+.
  • Historical road deaths: lowest year 1923 (59 deaths), rising to a peak in 1973 (843 deaths, the highest year on record), then declining with fluctuation to 341 deaths in 2023.
  • Road deaths per 10,000 vehicles fell earlier and more steadily (from ~8-9 in 1936 to below 1 by 2016) than deaths per 100,000 population (which peaked at ~28 around 1973 before falling to ~6-7 by 2016) — raising the question of which denominator (e.g. distance travelled) is most meaningful for comparing rates over time.
  • Transport mortality (2002-2019) in those aged 28 days to 24 years: the 15-19 and 20-24 age groups show much higher and more variable mortality (roughly 15-30 deaths per 100,000, peaking around 2004-2005 at ~27-29, generally declining to below 15 by the late 2010s) than younger age groups (<1 to 10-14 years), which remained low (mostly under 5-7 per 100,000) throughout.

History of NZ road safety legislation

Timeline of key interventions:

  • 1965: all new motor cars, station wagons and light trucks must be fitted with safety belts.
  • 1967: demerit points system introduced; the American-based Defensive Driving Course introduced to NZ.
  • 1969: breath and blood alcohol tests introduced; minimum tread depth for pneumatic tyres prescribed.
  • 1970: speeding infringements introduced.
  • 1973: NZ records its highest-ever annual number of road deaths.
  • 1975: front seatbelts become compulsory.
  • 1978: blood alcohol limit reduced to 80 mg/100 mL.
  • 1979: compulsory seat belt age lowered to eight years old.
  • 1984: NZ Police start random roadside breath alcohol testing.
  • 1987: NZ becomes the first country in the world to introduce a Graduated Driver Licensing (GDL) system.

Case study: young drivers and Graduated Driver Licensing (evidence-based policy)

This example works through the public health framework stages in sequence.

  • 1985/86: review of evidence relating to young driver crashes (defining/describing the problem).
  • 1987: introduction of GDL for those aged 15-24, with three stages — learner licence (supervised driving), restricted licence (restrictions on night driving and carrying passengers), and full licence. GDL was accompanied by a reduced BAC limit of 0.03 mg% for this group. Ongoing evaluation of GDL followed (developing and evaluating interventions).
  • 1999 modifications, after evaluation: GDL extended to all new drivers (not just those aged 15-24); “L” plates introduced for learners; “automatic only” restricted licences introduced; a new driving test introduced.
  • 2000 evaluation finding: teenage drivers’ high relative risk means they reach risk levels commonly regarded as unacceptable in road safety even at their then-current legal BAC limit of 30 mg/dL, particularly when more than one passenger is carried.
  • Keall, Frith & Patterson (Accident Analysis & Prevention, 2004) modelled adjusted risk (95% CI) of night-time fatal driver injury by BAC and age group, relative to a sober driver aged 30+ with one passenger: at BAC 0, risk was already elevated for younger drivers (age 15-19: 5.3, 20-29: 3.0, 30+: 1.0 reference); risk rose steeply with BAC and fell with age at every BAC level, reaching its highest values at BAC 100 mg/dL (age 15-19: 174.5, 20-29: 101.1, 30+: 33.2).
  • Further modifications following ongoing evaluation: 2011, zero alcohol limit introduced for drivers under 20; 2011, minimum driving age increased from 15 to 16.

Road to Zero and recent developments

  • Road to Zero vision: a New Zealand where no one is killed or seriously injured in road crashes — no death or serious injury while travelling on NZ roads is acceptable.
  • Its focus areas map onto the epidemiological triad: environment factors (infrastructure improvements and speed management), agent factors (vehicle safety and work-related road safety), and host factors (road user choices), plus system management reflecting international best practice. Its principles echo the Safe System approach (shared responsibility, designing for human vulnerability, planning to fail safely, evidence-based and evaluated actions).
  • Casualties by road user type (2018, Ministry of Transport): drivers 182, passengers 92, motorcyclists and their passengers 54, pedestrians 41, cyclists 5, bus passengers 2, other 1.
  • Contributing factors to deaths and serious injuries (2017): alcohol and drugs (130 deaths / 446 serious injuries); speed (97 deaths / 647 serious injuries); fatigue (36 deaths / 142 serious injuries); distraction (8 deaths / 49 serious injuries).
  • “Vision Zero in action”: before/after example at Mangere, where a straight open road was narrowed with a landscaped median/roundabout treatment; lower speed limits (e.g. “30 zone” markings) are argued to make towns and cities better places to live as well as safer.
  • December 2023: the government amended speed limit rules to stop “blanket” speed limit reductions, requiring Road Controlling Authorities to weigh economic impacts and community views alongside safety, and introducing interim speed limits on roads near schools during pick-up/drop-off times. By January 2025, 38 sections of the state highway network had reversed to previous (higher) speed limits, with 49 more sections going to public consultation; a road safety advocacy group took legal action over the rollback, and reaction was mixed, with some calling the changes “reckless.”
  • 2024 provisional figures: 289 road deaths in New Zealand, the first year the annual road toll fell below 300 since 2014, equating to 5.4 deaths per capita — the lowest rate of road deaths per head of population since the 1920s, and 52 fewer deaths than the previous year.

Self-test

  1. Give the ICD definition of injury, including how the timing of its onset and manifestations is described.
  2. Explain what is meant by an injury’s “external cause” and give an example of how it differs from what is coded for the injury itself.
  3. Describe the epidemiological triad and how its three factor types relate to each other.
  4. List the stages of the public health framework in order, as a cycle.
  5. What proportion of worldwide injury deaths (2012) were due to road traffic injuries, and for which age group are road traffic injuries the leading cause of death?
  6. Describe the injury pyramid and what it shows about costs and disability.
  7. State the WHO Global Plan’s target for reduction in road traffic deaths and serious injuries by 2030, and name the approach it calls for.
  8. List the six domains of the Safe System approach.
  9. State the WHO best-practice BAC limits for the general driving population and for novice drivers.
  10. Describe the three stages of New Zealand’s Graduated Driver Licensing system as introduced in 1987, and the BAC limit that accompanied it.
  11. Using the Keall et al. findings, describe how adjusted risk of night-time fatal driver injury varies with BAC and with age group.
  12. List the modifications made to GDL in 1999, and the two further changes made in 2011.
  13. In the 2017 New Zealand data, which contributing factor had the highest number of associated deaths, and which had the highest number of associated serious injuries?
  14. Distinguish the population-based and vehicle-based road death rate trends in New Zealand from 1936 to 2016, and explain the question this comparison raises.
  15. Describe how the Road to Zero focus areas map onto the epidemiological triad’s three factor types.

Answers

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