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Traffic Safety  and the Smart Growth Street Network Norman W. Garrick University of Connecticut Wesley Marshall University...
What Does a Smart Growth  Street Network look Like?
Or this?
Or this?
Or this?
Characterizing Street Networks <ul><li>Streets networks are devilishly complicated </li></ul><ul><li>The possible variatio...
California Cities Study of Street Networks Does the Street Network Matter? Twenty-four Cities
Davis, CA 14 % of people ride to work
Davis, CA Road Fatality Rate:  1 per 100,000
Road Fatality Rate for All 157 California Cities Over 40,000 number per 100,000 population 0.0 17.3
Road Fatality Rate for All 157 California Cities Over 40,000 number per 100,000 population
 
Risk of Fatality (Fatalities as % of Injuries)   California Cities of 40,000 to 120,000
Chance of Pedestrian Fatality vs. Impact Speed
Adapted from Stephen Marshall Pre-1950’s Post-1950’s Evolution of the Street Network
 
 
FHA Technical Bulletin No. 7 (1938) Planning Profitable Neighborhoods
<ul><li>According to the FHA the grid layout was </li></ul><ul><li>Monotonous </li></ul><ul><li>Had Little Character </li>...
Research
Evolution of the Street Network
Characterizing the the Street Network <ul><li>Shape and Configuration </li></ul><ul><li>Street Network Scale </li></ul><ul...
Citywide Street Network Neighborhood Street Network Linear Tree Grid Tributary Radial Grid Tree Adapted from Stephen Marsh...
550 Intersections per Square Mile Network Scale
110 Intersections per Square Mile Network Scale
45 Intersections per Square Mile Network Scale
Link-to-Node Ratio = 1.61  Link-to-Node Ratio = 1.13  Link-to-Node Ratio = 1.16  Network Connectivity
<ul><li>Street Network Properties </li></ul><ul><li>Street Design Properties </li></ul><ul><ul><li>Average Total Number of...
Safety Analysis Based on Geo-coding  230,000  Accident Records in 24 California Cities
Safety and Travel Choice Analysis done for  1040  Census Block Groups  24 California Cities
versus
versus Risk of Severe Injury or Fatality*  Chance of being Severely Injured  30%  Higher Chance of being Killed  50%  High...
Odds of Dying in a Road Accident  based on Intersection Density* 1 in 200 1 in 500 *Given that an injury occurred
Does Street Network Matter for Safety? <ul><li>The street network plays a huge role in terms of traffic safety </li></ul><...
What About Connectivity? <ul><li>Street pattern types that are more connected are safer  </li></ul>Safer Less Safe Within ...
 
Clipping the Grid in Berkeley Very high connectivity can be a mixed blessing
Why Does Street Network Matter? <ul><li>Why does street network matter for safety? </li></ul><ul><li>Understanding this is...
Design for Safety <ul><li>The two most important characteristics of  </li></ul><ul><li>the street network in designing for...
Connected? Yes… based on convention matrices
Functionally Connected for Walking? No…. Each neighborhood is an isolated pod
Traffic Safety and Smart Growth <ul><li>The same street design features that support traffic safety also </li></ul><ul><ul...
Percentage of People  Walking,  Biking  or   Taking Transit
Percentage of People  Walking,  Biking  or   Taking Transit Effect of Intersection Density for Cul-de-sac Network
Percentage of People  Walking,  Biking  or   Taking Transit Effect of Intersection Density for Gridded Network
Street Networks for Smart Growth <ul><li>There is no one type of ‘smart growth street network’ </li></ul>
Smart Growth Street Network? Yes
Smart Growth Street Network? No
What is a Smart Growth Street Network? No
Smart Growth Street Network? Yes
Connectivity Standards <ul><li>A handful of jurisdictions have enacted connectivity standards </li></ul><ul><li>Connectivi...
<ul><li>After years of ignoring the role of street network on traffic safety we are beginning to build a body of knowledge...
<ul><li>Great cities are built on the foundation of a Great Street Network </li></ul>
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Smart growth 2011 street network and safety

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How street network patterns affect traffic safety and travel patterns

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Smart growth 2011 street network and safety

  1. 1. Traffic Safety and the Smart Growth Street Network Norman W. Garrick University of Connecticut Wesley Marshall University of Colorado - Denver
  2. 2. What Does a Smart Growth Street Network look Like?
  3. 3. Or this?
  4. 4. Or this?
  5. 5. Or this?
  6. 6. Characterizing Street Networks <ul><li>Streets networks are devilishly complicated </li></ul><ul><li>The possible variations are infinite and even subtle differences can have a huge impacts </li></ul><ul><li>Street networks simultaneously operate at numerous geographic scales while serving many different – some times conflicting - functions </li></ul><ul><li>The common descriptors are not all that good for illuminating the differences between networks </li></ul>
  7. 7. California Cities Study of Street Networks Does the Street Network Matter? Twenty-four Cities
  8. 8. Davis, CA 14 % of people ride to work
  9. 9. Davis, CA Road Fatality Rate: 1 per 100,000
  10. 10. Road Fatality Rate for All 157 California Cities Over 40,000 number per 100,000 population 0.0 17.3
  11. 11. Road Fatality Rate for All 157 California Cities Over 40,000 number per 100,000 population
  12. 13. Risk of Fatality (Fatalities as % of Injuries) California Cities of 40,000 to 120,000
  13. 14. Chance of Pedestrian Fatality vs. Impact Speed
  14. 15. Adapted from Stephen Marshall Pre-1950’s Post-1950’s Evolution of the Street Network
  15. 18. FHA Technical Bulletin No. 7 (1938) Planning Profitable Neighborhoods
  16. 19. <ul><li>According to the FHA the grid layout was </li></ul><ul><li>Monotonous </li></ul><ul><li>Had Little Character </li></ul><ul><li>Uneconomical </li></ul><ul><li>Posed Safety Concerns </li></ul>
  17. 20. Research
  18. 21. Evolution of the Street Network
  19. 22. Characterizing the the Street Network <ul><li>Shape and Configuration </li></ul><ul><li>Street Network Scale </li></ul><ul><li>Street Network Connectivity </li></ul>
  20. 23. Citywide Street Network Neighborhood Street Network Linear Tree Grid Tributary Radial Grid Tree Adapted from Stephen Marshall, Streets & Patterns
  21. 24. 550 Intersections per Square Mile Network Scale
  22. 25. 110 Intersections per Square Mile Network Scale
  23. 26. 45 Intersections per Square Mile Network Scale
  24. 27. Link-to-Node Ratio = 1.61 Link-to-Node Ratio = 1.13 Link-to-Node Ratio = 1.16 Network Connectivity
  25. 28. <ul><li>Street Network Properties </li></ul><ul><li>Street Design Properties </li></ul><ul><ul><li>Average Total Number of Lanes </li></ul></ul><ul><ul><li>Average Outside Shoulder Width </li></ul></ul><ul><ul><li>Raised Median </li></ul></ul><ul><ul><li>Painted Median </li></ul></ul><ul><ul><li>On-Street Parking </li></ul></ul><ul><ul><li>Bike Lanes </li></ul></ul><ul><ul><li>Raised Curbs </li></ul></ul><ul><li>Travel and Activity Level </li></ul><ul><li>Distance from City Center </li></ul><ul><li>Income </li></ul><ul><li>Mix of Land Use </li></ul>Variables included in Our Safety and Travel Choice Models
  26. 29. Safety Analysis Based on Geo-coding 230,000 Accident Records in 24 California Cities
  27. 30. Safety and Travel Choice Analysis done for 1040 Census Block Groups 24 California Cities
  28. 31. versus
  29. 32. versus Risk of Severe Injury or Fatality* Chance of being Severely Injured 30% Higher Chance of being Killed 50% Higher *Given that an injury occurred
  30. 33. Odds of Dying in a Road Accident based on Intersection Density* 1 in 200 1 in 500 *Given that an injury occurred
  31. 34. Does Street Network Matter for Safety? <ul><li>The street network plays a huge role in terms of traffic safety </li></ul><ul><li>Street density seems to be the most important factor </li></ul><ul><li>Street network configuration is also important </li></ul><ul><li>The results with respect to ‘connectivity’ are a bit more complicated </li></ul>
  32. 35. What About Connectivity? <ul><li>Street pattern types that are more connected are safer </li></ul>Safer Less Safe Within each type of street pattern increasing connectivity – measured by link-to-node ratio - was not correlated with improved safety
  33. 37. Clipping the Grid in Berkeley Very high connectivity can be a mixed blessing
  34. 38. Why Does Street Network Matter? <ul><li>Why does street network matter for safety? </li></ul><ul><li>Understanding this issue is important for helping us to understand how to develop a new approach for designing street network </li></ul><ul><li>Street network affects </li></ul><ul><li>Speed control </li></ul><ul><li>Travel mode choice and VMT </li></ul><ul><li>Traffic distribution </li></ul><ul><li>Speed control reduces accident severity </li></ul><ul><li>More diverse mode choice and good traffic distribution reduces the demand for road capacity and means that we are more likely to keep the streets to a human scale </li></ul>
  35. 39. Design for Safety <ul><li>The two most important characteristics of </li></ul><ul><li>the street network in designing for safety are </li></ul><ul><ul><ul><li>Dense (Fine Grained) Fabric </li></ul></ul></ul><ul><ul><ul><li>Functional Connection for walking within and between neighborhoods </li></ul></ul></ul>
  36. 40. Connected? Yes… based on convention matrices
  37. 41. Functionally Connected for Walking? No…. Each neighborhood is an isolated pod
  38. 42. Traffic Safety and Smart Growth <ul><li>The same street design features that support traffic safety also </li></ul><ul><ul><li>Promote use of active transportation </li></ul></ul><ul><ul><li>Reduce VMT </li></ul></ul><ul><ul><li>Create value </li></ul></ul><ul><li>In other words, a safe street network is also a smart growth street network </li></ul>
  39. 43. Percentage of People Walking, Biking or Taking Transit
  40. 44. Percentage of People Walking, Biking or Taking Transit Effect of Intersection Density for Cul-de-sac Network
  41. 45. Percentage of People Walking, Biking or Taking Transit Effect of Intersection Density for Gridded Network
  42. 46. Street Networks for Smart Growth <ul><li>There is no one type of ‘smart growth street network’ </li></ul>
  43. 47. Smart Growth Street Network? Yes
  44. 48. Smart Growth Street Network? No
  45. 49. What is a Smart Growth Street Network? No
  46. 50. Smart Growth Street Network? Yes
  47. 51. Connectivity Standards <ul><li>A handful of jurisdictions have enacted connectivity standards </li></ul><ul><li>Connectivity standards by themselves will not necessarily produce safer communities or smart growth communities </li></ul><ul><li>We need more focus on the issues of </li></ul><ul><li>street network scale and functional connectivity </li></ul>
  48. 52. <ul><li>After years of ignoring the role of street network on traffic safety we are beginning to build a body of knowledge – we need to embrace the complexities of the issues </li></ul>
  49. 53. <ul><li>Great cities are built on the foundation of a Great Street Network </li></ul>

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