1. 1 Snowy / Icy Road Conditions and Crashes: What IS the Relationship? Marc Briese, P.E., PTOE Office of Traffic, Security, and Operations (OTSO)

2. 2 Brief History of Topic “There are more crashes in the winter, and specifically during snow events, but fewer Fatal and Life Changing crashes during snow events.” Historically, popular belief dictated the following Hypothesis:

3. 3 Brief History of Topic, cont. 2003-2004 Winter, Mn/DOT changed to new innovative plowing policy  cost savings. Shoulders and Medians cleared ‘day after’ Target for achieving bare pavement NOT changed (OT ok if needed) As a result of change, Media and others ask: “What will be the effect of this change on traffic safety?” Unfortunately, actual before/after analysis not possible  lack of data

4. 4 Instead, analysis concentrates on: WHAT IS EFFECT OF SNOWY/ICY ROADS ON TRAFFIC SAFETY? Brief History of Topic, cont. - Results may shed light on potential impacts of any change in snow and ice removal efforts.

5. 5 Inherent Limitations Exposure Tough to Measure (be conservative)  Vehicle Miles Traveled, fewer discretionary trips  Actual amount of time where roads are snow or ice covered  Could have snowed 5” at MSP Airport, and 0” in 2/3 of metro area, or vice versa Winter to Winter Comparisons are Tough  Snowfall varies greatly from winter to winter (1990’s varied from 34” to 89”)  Bridge/road icing happens under very specific, but not easily identifiable, conditions  Vehicle fleet continuously changing

6. 6 Introduction Current thinking from earlier: - “There are more crashes in the winter, and specifically during snow events, but fewer Fatal and Life Changing crashes during snow events, due to reduced speed.” Intent of Analysis is to prove or disprove this hypothesis. Analyses for Trunk Highways ONLY (ISTH, USTH, MNTH).

7. 7 Introduction cont. Part I: District Comparison - winter vs summer months Part II: Statewide Comparison - winter vs summer and road conditions Part III: Metro Division Days with Snow - ~150 days (1996-1999) with snowfall >= 0.1” Part IV: Statewide Comparison - road conditions + weather conditions

8. 8 Introduction Cont. Crash Severity Defined* * Note: crash severity is determined by most severe injury Fatal (F) – one or more people killed ‘A’ Severity – incapacitating injury - E.g. severe laceration, broken/distorted limbs ‘B’ Severity – non-incapacitating injury - E.g. minor laceration, bruises, bump on head ‘C’ Severity – possible injury - E.g. momentary unconsciousness, claimed injury PD – property damage only

9. 9 Safety Analysis, Part I 2000-2002 There ARE more crashes, of all severity, in winter months.

10. 10 Safety Analysis, Part I cont. 2000-2002 There ARE fewer Fatal and ‘A’ Severity crashes in a typical winter month.

11. 11 Safety Analysis, Part II 2000-2002 Blanket Assumption: 20 full days of snow/ice covered conditions (13% of winter months) Overall, Snow/Ice Road condition F and ‘A’ crashes represent a small % of all F and ‘A’ crashes, 13%. But in winter months, they make up ~30%.

12. 12 Safety Analysis, Part II cont. 2000-2002 Outstate Graphics

13. 13 Safety Analysis, Part II cont. 2000-2002 Metro Graphics

14. 14 Safety Analysis, Part II cont. 2000-2002 SO WHAT DO THE PAST THREE SLIDES TELL US? Crashes on Snowy/Icy Roads = small % of F and ‘A’ crashes overall, but large % during winter months. From Earlier, roads are snow/ice covered full 20 days per winter = 13% of the time during winter months. 30% of the F and ‘A’ Crashes occur during snowy/icy road conditions  LARGE over-representation – 2x more than expected (conservatively).

15. 15 Safety Analysis, Part III 1996-1999 Climatology data take from National Weather Service station at Minneapolis – St. Paul International Airport Considered days with Snowfall >= 0.1” BUT Again – inherent problems:  Could have snowed 5” at MSP Airport, and 0” in 2/3 of Metro area, or vice versa  Sample size of ‘snowy days’ is limited (148 with >= 0.1” over 4 years)

16. 16 Safety Analysis, Part III cont. 1996-1999 As Snowfall Increases, Number of Fatal and A Severity Crashes increases (Metro Crashes)

17. 17 Safety Analysis, Part III cont. 1996-1999 In comparison, Rainfall appears to affect crashes less than snow. (Metro Crashes)

18. 18 Safety Analysis, Part IV 1998-2002 Road and Weather Conditions are Reported on the Minnesota Police Crash Report. Road conditions either snowy or icy, but weather condition NOT listed as snow or freezing rain/sleet/hail. Primarily when: After snow event when it’s no longer snowing, but road not restored to bare pavement yet. Bridge decks icy at dawn or black ice. Drifting or Blowing Snow

19. 19 Safety Analysis, Part IV cont. 1998-2002 From earlier, 2x Over-representation of F & A crashes during poor road conditions Opportunity to prevent 43 outstate, 19 Metro F & A crashes per year

20. 20 Conclusions I. More crashes (of all severity) in winter months. Fewer F and ‘A’ crashes in winter months.  Both consistent with popular belief. II. With snowy/icy road conditions, there are higher number of F and ‘A’ crashes than expected – over TWICE the number expected. III. By analyzing Snow Events in the Metro, it was found that there is a positive relationship between snowfall amount and the number of Fatal + A Severity crashes.

21. 21 IV. There is potential to prevent F and ‘A’ Crashes during snowy/icy road conditions. Increased efforts statewide could prevent up to 62 F & A crashes per year. Further study necessary to determine appropriate strategies for each district. Possible approaches include: - Return THs to bare pavement more quickly - Be more aggressive in anti-icing - Improved Education to public regarding relative dangers of traveling during snowy/icy weather - Increased Enforcement Efforts - Increased awareness for EMS Conclusions cont.

22. 22 “Snowy/icy road conditions appear to be associated with a higher than expected frequency of ALL crash severities, including Fatal and Life Changing crashes.” Conclusions cont. As a Result of these analyses, old hypothesis appear to be incorrect. Analyses suggest: