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Investigating Crash Interaction of Younger and Older Drivers

Investigating Crash Interaction of Younger and Older Drivers. Hossein Naraghi. Masters Thesis Defense October 15, 2004. Iowa State University. Overview. The problem Demographics Risk assessment Statewide interaction analysis Causal factors Spatial analysis Geometric analysis

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Investigating Crash Interaction of Younger and Older Drivers

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  1. Investigating Crash Interaction of Younger and Older Drivers Hossein Naraghi Masters Thesis Defense October 15, 2004 Iowa State University

  2. Overview • The problem • Demographics • Risk assessment • Statewide interaction analysis • Causal factors • Spatial analysis • Geometric analysis • Temporal analysis • Conclusions, limitations, & recommendations

  3. The Problem

  4. Younger drivers (Y) • Young Drivers • Inexperience • Poor judgment • Risk taking behavior

  5. Older drivers (O) • Older Drivers • Reduction in physical abilities • Reduction in cognitive capabilities • “Too” careful?

  6. Compound effect? What will occur as a result of interaction of these two critical age groups?

  7. Licensed Drivers by Age Group Iowa has 9%more Young Iowa has 20% more Older Iowa has 50%more Young Drivers Iowa has 18% more Older Drivers

  8. Iowa older driver trends • Total population is relatively flat • Older driver population increase caused by … • More older population • Higher % licensed

  9. Iowa older driver trends • In 1970 only 60% of older population was licensed (240,000) • In 2000 80% was licensed (350,000, or 17% of all drivers) • In 2025 if 80% are licensed (500,000, or 24% of all drivers) • In 2025 if 87% are licensed (550,000, or 26.5% of all drivers)

  10. Iowa younger driver trends • Decrease (%) from 1970’s to early 1990’s • 10.7% increase in younger population from 1991-2000 (compared to 4.8 % increase in total population) • In 2000, 157,000 younger drivers were licensed (7.4% of all drivers)

  11. Iowa Y-O driver trends Assuming no increase in percentage of younger drivers … in 2025, as much as 35% of Iowa drivers will be older & younger drivers (compared to ~25% in 2000) In some parts of the state, this is already occurring …

  12. Over 20 percent Older drivers (2000) 53 counties have 20% or higher

  13. Over 10 percent younger drivers (2000) 23 Counties have 10% or higher

  14. Over 1/3 younger and older drivers (2000) 20 Counties Have Older & Younger Drivers > 1/3 of Driving Population

  15. Risk Assessment

  16. How much do these cohorts drive?

  17. Iowa Y & O crash overrepresentation E = 27029 H =73963 Interpretation: young drivers are 3.9 times as likely to be involved in a 2-veh crash as compared to the “average” driver Ref # 1: 2001 National Household Travel Survey Ref # 2: Iowa Crash Facts 2000 Ref # 3: Iowa DOT crash database

  18. Statewide Analysis

  19. Statewide Interaction of Younger and Older Drivers The unadjusted probability that a driver involved in a 2-vehicle crash will be from a particular age group is the fraction of VMT driven by that age group …

  20. What is expected? Assuming independence (e.g., the fact that an older driver is involved in a crash does not affect the likelihood of the other driver coming from a particular age group), the expected number of 2-veh crashes between age groups is … )*( )* ( e.g., E(Y-O) = 0.047 * 0.093 * 34,264 = 150

  21. Expected 2-veh crashes,Unadjusted Assuming independence, the joint probabilities are …

  22. Statewide Interaction of Younger and Older Drivers • Based only on VMT YO crashes are clearly overrepresented… • however, how much of this is due to the fact that older and younger drivers as groups are each overrepresented???

  23. Statewide Interaction of Younger and Older Drivers The adjusted probability that a driver involved in a 2-vehicle crash will be from a particular age group is …

  24. What is expected? Again, assuming independence … The expected number of 2-veh crashes between age groups is now … )*( )* ( e.g., E(Y-O) = (0.18)*(0.11)*(34,262) = 659

  25. Expected 2-Veh crashes, adjusted for age

  26. Statewide, we observe that Y-O crashes are underrepresented

  27. Chi-square is used to make sure differences observed are significant Unadjusted Analysis 41,566 is much larger than the critical value of about 16 for 3 degrees of freedom and 99.9% significance level

  28. Adjusted Analysis 258 is also much larger than the critical value of about 16 for 3 degrees of freedom and 0.001probability of exceeding the critical value

  29. Causal Factors

  30. Major Cause of 2-vehicle crashes

  31. Driver contributing factors

  32. One Passenger • 2 or More Passengers Younger16% More than Older 27% More than All 2-veh Younger 225% More than Older 30% more than all 2-veh

  33. Spatial Analysis

  34. County by County Analysis

  35. Y-O representation (adjusted) Sample size >= 5 Statewide YO under-representation is 18%

  36. Proximity to High Schools at 1.5 mile distance from high schools: About 72% of all Y-O crashes occur Y-O crashes have the highest percentage of all 2-veh crashes Y-O crashes are 13% higher than all 2-veh crashes

  37. Urban/Rural Analysis

  38. Highway Geometry

  39. Y-O crashes most likely at intersections Y-O crashes are about: 20%higher than Y-Y crashes 8%higher than O-O crashes 17% higher than M-M crashes

  40. Intersection functional class Comparing Y-O to all 2-veh crashes

  41. Are divided expressways a problem? e.g. 6.83% of all Y-O Crashes occur at intersections of divided roads

  42. Temporal Analysis

  43. 3:00-4:00 PM is critical

  44. When Do Older and Younger Drivers Crash?

  45. Conclusions • Y-O under-represented at statewide level, … why? • Driving in different places and at different times? • Y-O significantly over-represented in some counties • High risk characteristics of Y & O drivers may be most problematic at intersections • After school hours are the most risky time of driving for both age groups

  46. Conclusions (cont.) • Presence of passenger (esp. 2 or more) increases crash risk of younger drivers, but may have a beneficial effect on older drivers • Older drivers experiencing more difficulty at divided expressway intersections than their younger counterparts - Come across younger drivers is the most difficult

  47. Limitations • Lack of local exposure (VMT) data • By age group in Iowa (used US averages) • No Iowa, county, or spatial + time of day exposure data • No knowledge of proportion of drivers in each age group that carry passenger(s)

  48. Recommendations • Limit passengers for younger drivers • Educate older drivers about the benefit of a passenger • Educate older drivers about the risk associated with driving after school hours (they already know to avoid driving in congestion) • Collect more data (or at least a sample) on exposure, time of day, more stratified data (esp. for Y & O)

  49. Future Research • Investigating if particular types of crashes occur more often in Y-O crashes • e.g. rear-end, head-on, left turn, and sideswipe • Investigating the overrepresentation in Y-O crashes in the vicinity of high schools by time of day and distance from high schools • The over-involvement in Y-O crashes by gender • Investigating safety implications of Y-O crashes by roadway functional class • e.g., expressways, county roads, and city streets • Comparing Y-O overrepresentation in rural and urban areas

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