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How to influence road user behaviour by police enforcement? PowerPoint PPT Presentation

How to influence road user behaviour by police enforcement?. A contribution to an answer from research. Fred Wegman SWOV Institute for Road Safety Research The Netherlands. “Car drivers defeated by speed cameras”. About SWOV Institute for Road Safety Research .

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How to influence road user behaviour by police enforcement?

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How to influence road user behaviour by police enforcement?

A contribution to an answer from research

Fred Wegman

SWOV Institute for Road Safety Research

The Netherlands

“Car drivers defeated

by speed cameras”

About SWOV Institute for Road SafetyResearch

  • Independent, non-profit institute, founded in 1962

    • Aims to improve road safety by ‘evidence based’ knowledge

    • By carrying out research, and by

    • Knowledge dissemination to road safety professionals

  • Subsidy from Dutch Ministry of Transport and national and international contracts

  • Current staff: 60 ftu

Structure of this presentation

  • Why do we have road crashes, how to prevent them (best)?

  • How does police enforcement fit in a road safety strategy?

  • Why police enforcement should work to reduce the number of casualties?

  • How to set priorities for police enforcement?

  • Conclusions and recommendations

A. Why do we have road crashes

and how to prevent them (best)?

…just one accident

  • 18 years old

  • Just passed his/her driving test

  • Saturday night

  • Drives his/her friends home

  • …from a party

  • Windy dyke

  • It’s raining

  • Misjudges a bend

  • Drives too fast

  • Trees alongside the road


  • A young, inexperienced driver

  • Distracted by the passengers

  • Driving at night

  • In the rain

  • With inappropriate speed

  • An unexpected sharp bend

  • Bald tyres

  • Trees in a bend

  • Don’t look for one single cause or one culprit!

Traditional approach

  • Define high risk groups/conditions and take cost-effective countermeasures, e.g.

    • Young novice drivers

    • Black spots

    • Vehicle inspection

    • Violators, recidivism

  • Certainly progress can be made in many countries, but we reach a stage that this will be less effective/efficient

  • We need a paradigm shift!

    • examples from three countries

Reasons for (fatal) injuries: Sweden

  • Excessive force: road user makes an error

  • Excessive risk: injured due to insufficient personal protection

  • Beyond system restrictions: violating regulationsSweden: two-thirds due to excessive forceSRA (

Discussion on a paradigm shift in the UK

Relative contribution

Driver failures:


Rod Kimber TRL (2003)

New road safety paradigm in NL

  • Road system is inherently unsafe

  • Human errors are and will always be made

  • Making human errors less likely by:

    • Eliciting the desired/safe behaviour

    • Making undesired error less likely

  • Forgiving human error by:

    • Providing an opportunity to correct an error

  • Reducing the consequences, once a crash has become inevitable, by system design based on ‘human tolerance’

  • English version published in November 2006

  • Copies free downloadable from


Sustainable Safety

  • Philosophy developed in early nineties by SWOV

  • Basis of the Dutch road safety policy

  • Implementation since mid nineties

  • Update in 2006

B. How does police enforcement fit in

a road safety strategy?

Speed management

Current speeding


Speed indicators


Dynamic relations

Vehicles: top speed/

impact speed

Speed and

Road crashes

Attitudes to speeding

Speed and road design


Vehicle measures

Speed limits



Different methods to classifyinterventions (source Tony Bliss)

Enforcement in a road safety strategy

  • Using long term vision, system-wide strategies and targets + targeted programmes

  • Implement measures that are known to be correct and effective (and efficient)

  • Use effective delivery mechanisms (regionally and locally); look for partnerships

  • Compliance with road safety rules is a key safety strategy: enforcement!

C. Why police enforcement should work to reduce the number of casualties?

Evaluation of Traffic Law Enforcement

  • Traffic Law Enforcement and risk of death(Redelmeier, Tibshirani and Evans, The Lancet, 2003)

  • Method: 8975 fatal crashes in Ontario, Canada (11 years), 21,500 driving convictions, case-crossover study

  • Findings: risk of a fatal crash in the month after a conviction was about 35% lower than in a comparable month with no conviction. No significant benefits after 3-4 months.

  • So: enforcement helps!

Relationship between violationsand risks?

  • The correlation between violation and crash records is positive, but small (r=.2)

  • The stability of individual records from one year to another is small

  • Violators will experience more crashes, but for individuals the prediction is useless

  • Previous violations better predict future violations and previous crashes predict better future crashes

  • A small group commit many violations, but account for a small fraction of recorded offences and crashes

Assumed mechanism of police surveillance

Violations and risks

  • Many well known main risk factors (related to violations)

  • Speed, alcohol (+drugs), seat belts, child restraints, crash helmets, red light running, technical defects, commercial traffic, fatigue, aggressive driving/road rage, short headways, mobile phones, etc.

Two risk factors in road traffic (Borkenstein US + Kloeden Australia)

How to set priorities for police enforcement?

Which violations to select to betargeted by enforcement?

  • How do violations contribute to risk increase?

  • Which violations are enforceable?

  • Which effects of enforcement on behaviour?

  • Which effects of changed behaviour on crash reduction?

  • How to incorporate cost-benefit considerations in priority setting?

Violations and risks

  • Most important violations according to their contribution to road accident fatalities in the Netherlands:

    • Speeding: nobody higher than existing speed limits: 20-25% less fatalities

    • Drinking and driving: nobody above legal limit: 20-25% less fatalities

    • And all the other violations?

    • Total: 50%?

  • Which priorities?

D. How to set priorities for police enforcement?

Use evidence based knowledge

Speed management by enforcement

  • Speed cameras are more effective than physical policing methods

  • Speed cameras are more effective in reducing crashes inside urban areas than on rural roads

  • Fixed speed cameras are more effective in reducing speeds and crashes than mobile speed cameras

  • Speed cameras appear to have a distance halo effect

  • Physical policing in combination with randomization of police checks over road sections and times have a larger halo effects (minimally five times larger than that of speed cameras).

TRL review (Elliott and Broughton, 2005)

Three questions of priority setting

  • Which violations to select to be targeted by enforcement?

  • Which effects are expected of the deployment of enforcement manpower + technology and which methods of enforcement to select?

  • What to learn form evaluation studies on enforcement?

Distinguish three levels professionality

Police enforcement on three levels of professionalism

  • Ad hoc enforcement:

    • Short term operations (few weeks), few, specific locations and strong emphasis on catching offenders

  • Project bound enforcement:

    • Longer term planning (several months), often covers a certain route or number of locations and explicitly described aims, guided by evaluation efforts

  • Planned enforcement:

    • Annual plans, larger areas (regions, provinces), permanent operation, based on area-analysis, and evaluation results

General conclusions on priority setting

  • A lot of knowledge is available

  • Available knowledge is not always used in enforcement practices

  • Still major questions on distance- and time halo effects

  • More knowledge needed when scaling-up results of experiments

Deployment of enforcement manpower (I)

  • Nowadays based on: high number of crashes, high risks or high number of violations and judgement based on common sense about enforceability

  • Three approaches:

    • How to prevent per ‘unit of enforcement’ most fatalities/injuries (highest b-c ratio)

    • How to organise general deterrent best?

    • How to deal with hard-core behaviour and serious recidivism?

      Not very well researched, space for improvement

Deployment of enforcement manpower (II)

  • My personal opinion

    • Rely on random selection of persons, locations, and times of deployment, thus avoiding a (predictable) pattern (general deterrence)

    • Combined with efforts to detect main/heavy/frequent violators (specific deterrence)

    • Balance?

    • Methods?

Impact of enforcement on crashes (I)

  • Theoretical estimates based on enforcement inducing full compliance: 40-50%

  • Estimates based on empirical studies: about 10%

  • Estimates of some well implemented and sustained enforcement efforts: 20-25%

Impact of enforcement on crashes (II)

  • What to do to bring the 10% (observed effects) to 20-25% (potential effects)?

    • Better performance by the police: better use of knowledge, more funds, better organisation and management, better education, better motivation?

  • What to do to bring the 20-25% (potential effects) to 40-50% (full compliance)?

    • Better implementation of a road safety strategy: which interventions are effective, cost-effective, reduced return, acceptance by public and politicians?

E. Conclusions and recommendations

Conclusions and recommendations (I)

  • Non-compliance with traffic laws is massive in many countries, if not all, and is a major road safety problem

  • Non-compliance leads to additional deaths and injuries

  • Enforcement has a positive impact on compliance and is an important road safety intervention

  • Our theoretical basis of traffic enforcement is strong enough (through general deterrence and using specific deterrence, creating intrinsic motivation)

Conclusions and recommendations (II)

  • Enforcement should focus on those violations which can be prevented best by enforcement; best practices and knowledge transfer are needed

  • Enforcement should play a more integral role in road safety strategies instead of a stand alone role (not all violations should be prevented by enforcement only)

  • Scientific research can be instrumental to support enforcement authorities (by knowledge transfer and evaluation research)

  • A planned multi-year approach to enforcement should be set up, incorporating credibility, the whole enforcement chain and monitoring of results

Conclusions and recommendations (III)

  • More emphasis should be placed on the dose-response relationship of enforcement, also in research

  • Large and permanent increase in policing resources have a measurable positive effect on road safety

  • Investments in the quality of enforcement is needed to make it more effective, efficient, and credible;


  • Consider earmarking income from traffic tickets to enforcement activity (self-funding)

2020 Mortality rate

3 per 100,000?

Further progress, e.g. the Netherlands

Speed cameras: a cry for “REVENGE”

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