1. CE 635 - Typical crash rates and distributions
- Crashes that take the highest toll on human life

2. Rates …why? To compare locations
To decide if a location is at abnormal risk
Rate per million entering vehicles:
In-class calculation

3. In-class calculation
This should really be RHMVM, shouldn’t it?

7. Expected value analysis
Use only to compare “similar” sites (geometry, control, volume)
Problem: crashes are non-neg. count data (normal distribution does not apply)
In-class calculation

8. Cluster analysis
E.g., if a site has one right-angle, two rear-end and 6 left-turn crashes, one might say the left-turn crashes represent a cluster
But … what if the # of left turns is very high … then, is 6 high?
Need exposure data
Must usually use good engineering judgment

9. High Crash Location Methods
Frequency
Rate
Severity/Cost
Some combination
Iowa DOT uses .2F+.2R+.6C
Critical Rate Factor method
Empirical Bayes

10. Critical Crash Rate Factor method
Error: this should say Z, not S
For derivation of equation and interpretation of terms, see link

14. Next step: engineering study at sites

17. Summarizing crash data
Severity, e.g., KABCO, MAIS
Type
Time Periods
Hour
Day
Month
Contributing
Circumstances
Environmental
Conditions
a) light condition
b) surface condition

18. Typical crash rates Iowa data for risk by road type
Oregon crash rates (compare to Iowa)
Source: NCHRP Web Only Document 126
Guidelines for using NC crash rates
Crash rate discussion

19. Aussie rates – compare road types

24. European crash rates by road type
Low traffic flow roads – there are significant differences in fatal and
serious accident rate between roads with less than 10,000 Average
Annual Daily Traffic (AADT), roads with 10,000 to 20,000 AADT, and
roads with more than 20,000 AADT. (The ratio of these differences is
about 2.3:1.8:1);
Note: to convert /bvkm to /HMVM, multiply by ~6 (Iowa K+A+B crash rate per HMVM in ~60, much lower than the numbers presented above for Europe if you multiply them by 6)

26. Kentucky Intersection Crash Rates

27. Massachusetts Intersection Crash Rates

28. From Oregon Study …

32. Crashes that take the highest toll on human life
Head-ons, Intersections, ROR, VRU
Show iRAP video

33. Head-on collisions head-on crash.
Fatal Head On Accident Six Killed On US12 Near Morton WA
Truck crossing median – 7 fatals video

35. Intersections (junctions)
See: UMN captured crashes

36. Manner of collision

37. Run-off the road (ROR)

40. Vulnerable Road users Motorcycles, bikes, pedestrians
Bicyclists and Other Cyclists (DOT-HS )

41. Children