Safety in Numbers: Is It Real

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Safety in NumbersIs It Real?

• Richard Haggstrom, P.E.

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Blueprint Goals

• 50 increase in trips by 2010
• 50 decrease in fatality rates by 2010
• Increased funding for bicycle pedestrian safety
  and mobility

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Blueprint Pedestrian Safety Goal
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Artifact of Two Inverse Compound Variables?

• 1. Fatality Rate (RF)
• RF Pedestrian Fatalities / Pedestrian Exposure
• Pedestrian Fatalities / Ped Commuters
• FP / CP
• 2. Pedestrian Mode Share (MP)
• MP Pedestrian Trips / All Trips
• Ped Commuters / All Commuters CP / CA

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Smeeds Law
Smeeds law fitted to data from 62 different
countries (from Adams 1985)
Deaths/(1000 Vehicles)
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Hyperbole?
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XYConstant?
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Safety in Numbers for Vehicles?
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Tentative Conclusion (1)

• Safety In Numbers appears to be more sensitive to
  the specific formulation of the data than to the
  presence of inverse compound variables.

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John Foresters Claim Mode Share and Improved
Safety both Caused by Other Factors

• Climate
• Local economy
• Density
• Land use
• Cultural life
• Social attitudes
• Cyclist skill levels
• Street design
• Income levels

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Conclusion (2)

• Mathematical models can be useful even when
  causation has not (or cannot) be established
• From a policy perspective, it is important to
  know that increased walking and bicycling is
  correlated with increased safety for those modes,
  whether causal or not.
• It is necessary to expand and improve data
  collection on walking and bicycling.

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Seamless TransportationMeasuring Bicycle and
Pedestrian Activity in San Diego County and its
Relationship to Land Use, Transportation, Safety,
and Facility Type

• David Ragland, PhD, MPH
• Michael Jones, MCP

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2008 NHTS Add-On Survey
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National Household Travel Survey2008 Add-on
Program

• 18,000 Sample Size
• Bike, ped and transit mode shares valid for
  counties and larger cities
• Counts all trips, including combined trips, not
  just commute trips
• Custom questions (compare DHS survey)
• Data easily accessible by all users

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Who Uses the Survey Data?
Consultants
Governments
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Media
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Interest Groups
Universities
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Source National Household Travel Survey Data
Use An Overview Prepared by MacroSys Research
and Technology for the Bureau of Transportation
Statistics, 2005