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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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slide1

Investigating Crash Interaction of Younger and Older Drivers

Hossein Naraghi

Masters Thesis Defense

October 15, 2004

Iowa State University

slide2

Overview

  • The problem
  • Demographics
  • Risk assessment
  • Statewide interaction analysis
  • Causal factors
  • Spatial analysis
  • Geometric analysis
  • Temporal analysis
  • Conclusions, limitations, & recommendations
slide4

Younger drivers (Y)

  • Young Drivers
    • Inexperience
    • Poor judgment
    • Risk taking behavior
slide5

Older drivers (O)

  • Older Drivers
    • Reduction in physical abilities
    • Reduction in cognitive capabilities
    • “Too” careful?
slide6

Compound effect?

What will occur as a result of interaction

of these two critical age groups?

slide7

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

slide8

Iowa older driver trends

  • Total population is relatively flat
  • Older driver population increase caused by …
    • More older population
    • Higher % licensed
slide9

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)
slide10

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)
slide11

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 …

slide12

Over 20 percent Older drivers (2000)

53 counties have 20% or higher

slide13

Over 10 percent younger drivers (2000)

23 Counties have 10% or higher

slide14

Over 1/3 younger and older drivers (2000)

20 Counties Have Older & Younger Drivers > 1/3 of Driving Population

slide17

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

slide19

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 …

slide20

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

slide21

Expected 2-veh crashes,Unadjusted

Assuming independence, the joint probabilities are …

slide22

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???
slide23

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 …

slide24

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

slide27

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

slide28

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

slide33

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

slide36

Y-O representation (adjusted)

Sample size >= 5

Statewide YO under-representation is 18%

slide37

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

slide40

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

slide41

Intersection functional class

Comparing Y-O to all 2-veh crashes

slide42

Are divided expressways a problem?

e.g. 6.83% of all Y-O Crashes occur at intersections of divided roads

slide46

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
slide47

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
slide48

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)
slide49

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)
slide50

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
slide51

Thanks to

  • Dr. Reginald Souleyrette
  • Dr. Edward Kannel
  • Dr. William Q. Meeker, Jr.
  • Mr. Zachary Hans
  • Mr. Robert Thompson
  • The staff and students of CTRE