SLIDE 1
– Part 1
- What do we mean by validation?
- Product validation
– Previous product validation
- Process validation
– Previous process validation – Part 2
- Product validation in InDeV
Outline
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Validation of surrogate traffic safety indicators Carl Johnsson, PhD - - PowerPoint PPT Presentation
Validation of surrogate traffic safety indicators Carl Johnsson, PhD - - PowerPoint PPT Presentation
Validation of surrogate traffic safety indicators Carl Johnsson, PhD student, Lund University ICTCT Workshop 2016, Lund Outline Part 1 What do we mean by validation? Product validation Previous product validation Process
SLIDE 2
SLIDE 3
What do we mean by validation?
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www.indev‐project.eu
- Does an indicator actually “measure” the property you
want to measure
- Validity of an indicator means to what extent it
describes (un)safety
- Relation between accidents and conflicts
SLIDE 4
Product validation
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- Correlation between conflicts and accidents
- Number of observed or expected conflicts
- Number of recorded or expected accidents
SLIDE 5
- Linear correlation
- Number of reported accidents
- Number of observed conflicts
Previous product validation
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www.indev‐project.eu (TRRL, 1980)
SLIDE 6
Previous product validation
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- Hauer and Gårder (1986)
- Variance of the Accident‐to‐conflict ratio, VAR()
- ∗
- “a technique (method, device) for the estimation of
safety is “valid” if it produces unbiased estimates, the variance of which is deemed to be satisfactory.”
SLIDE 7
- Focusing on the variance of the Accident‐to‐conflict ratio
Previous product validation
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www.indev‐project.eu (Hydén, 1977)
SLIDE 8
- Linear correlation
– Lord (1996)
- Estimate the expected number of accidents using an accident
prediction model
- Number of observed conflicts
Previous product validation
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SLIDE 9
- El‐Basyouny & Sayed (2013)
– Two‐phase model
- Predict expected conflict rate using traffic volume, area type
etc.
- Predicted conflict rate used as input for negative binomial
safety performance function
Previous product validation
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SLIDE 10
- Before‐after approach
– Autey et al. (2012)
- Before‐after conflict study
– Sacchi et al. (2016)
- Collision‐based full Bayes
before–after safety evaluation
Previous product validation
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www.indev‐project.eu (Autey et al., 2012)
SLIDE 11
- Indicates the extent to which safety indicators can be used for
describing the process that leads to accidents
Process validation
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SLIDE 12
- In‐depth accident studies or accident investigations by the
police
– Brake‐marks measured – interviews with involved road users and witnesses
- Compare ”process” between accidents and conflicts
Process validation
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SLIDE 13
Previous process validation
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www.indev‐project.eu (Hydén, 1987) (Hydén, 1987)
SLIDE 14
- Video recorded accidents
- Compare event leading to accidents compared to events
leading to conflicts
Previous process validation
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SLIDE 15
Previous process validation
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www.indev‐project.eu (Saunier et al., 2011) (Saunier et al., 2011)
SLIDE 16
Part 2
Product validation in InDeV
SLIDE 17
- 21 signalized intersections in 6 countries
– Spain, Sweden, Denmark, Belgium, the Netherlands and Poland – 3 weeks of filming
- Focus on pedestrians and bicyclists
- Manoeuvre specific
– Low number of recorded accidents
Product validation in InDeV
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SLIDE 18
– Similar approach to Lord (1996)
- Expected number of accidents
– Adapt safety performance function (SPF) – Nation and manoeuvre specific
- Expected the number of conflicts
– Based on observed conflicts
- Focus on the variance of the Accident‐to‐conflict ratio
Product validation in InDeV
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SLIDE 19
Product validation in InDeV
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Expected number of accidents Expected number of conflicts
- Comparison of two different
methods to estimate safety.
SLIDE 20
Thank you very much for your attention!
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 635895
Visit us on www.indev‐project.eu
Carl Johnsson, PhD student, Lund University
SLIDE 21
- Suggested accident model in InDeV
– ∗
∗
- 1 & 2 will be estimated based on literature
Product validation in InDeV
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SLIDE 22
- Güttinger (1979)
– The relation between serious conflicts and accidents must be stronger than the relation between traffic volume and accidents. – The relation between serious conflicts and accidents must be stronger than the relation between people’s opinion regarding road safety and accidents.
Satisfactory validation
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