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Scientific Principles for Effective Road Safety Analysis

Scientific Principles for Effective Road Safety Analysis. Apply scientific principles to decision-making regarding road safety problem identification, countermeasure selection, and evaluation. 0. Major Topics. Rational vs. Pragmatic Style of Road Safety Research Regression-to-the-Mean

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Scientific Principles for Effective Road Safety Analysis

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  1. Scientific Principles for Effective Road Safety Analysis Apply scientific principles to decision-making regarding road safety problem identification, countermeasure selection, and evaluation. 0

  2. Major Topics • Rational vs. Pragmatic Style of Road Safety Research • Regression-to-the-Mean • Exposure Data • Safety Performance Functions • With-Without Rather than Before-After

  3. Rational Data and analysis Factual experience Estimates based on the effect on safety Pragmatic Lay beliefs Personal anecdotal experience Meeting standards means “safe” Rational vs. Pragmatic Styles

  4. Regression-to-the-Mean (RTM)

  5. Table 1.1 1974-1975 San Francisco Data Source: Hauer, E., 1986

  6. Table 1.1 1974-1975 San Francisco Data Source: Hauer, E., 1986

  7. Table 1.2 1975-1976 San Francisco Data Source: Hauer, E., 1986

  8. Table 1.3 1976-1977 San Francisco Data Source: Hauer, E., 1986

  9. Applying Exposure Data • Exposure – the amount of travel that underlies any observed number of crashes • Crash rate • Crashes/VMT • Fatalities/100 million VMT • Injuries/capita • Exposure should be related to crashes by a function

  10. SPF for Countermeasure Evaluation 1.2 X X X X XX X X 1.0 X X X X Crashes per unit time X 0.6 XX XXX X 0.4 X XX XX 0.2 Annual Driving Miles 1000 2000 3000 4000 5000 Safety 101

  11. SPF for Countermeasure Evaluation 1.2 X X X X XX X X SPF 1.0 X X X X Crashes per unit time X 0.6 XX XXX X 0.4 X XX XX 0.2 Annual Driving Miles 1,000 2,000 3,000 4,000 5,000 Safety 101

  12. SPFs show how changes in exposure alone can affect crash frequency or rates at any given entity Before-after does not account for changes in exposure and can lead to inaccurate measures of effectiveness With-without considers changes in exposure for more accurate problem identification, countermeasure selection, and evaluation With-Without Rather than Before-After

  13. Review • Rational vs. Pragmatic Style of Road Safety Research • Regression-to-the-Mean • Exposure Data • Safety Performance Functions • With-Without Rather than Before-After

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