Why Hikers & Bikers Should Avoid Cars, Trucks, and Trains

1. Why Hikers & Bikers Should Avoid Cars, Trucks, and Trains The Dynamics of Trauma in Vehicle Collisions Involving Pedestrians or Bicyclists Brian A. Donaldson Operations Supervisor Western Eagle County Ambulance District Eagle, Colorado brian@proEMSeducators.com Revised 2005

2. Ground Rules • Please place all electronic devices into a quiet or vibrate mode, if possible. • Be an active participant…you don’t want to listen to me for an hour! • Relax & enjoy yourself. • If you are easily offended, please locate the exit nearest your seat.

3. One Final Ground Rule What happens in St George… Stays in St George

4. Identify Newton’s Laws of Motion and the Conservation of Momentum Identify Estimated Vehicle Striking Speed based on Contact Damage Identify Probable Injuries based on Vehicle Striking Speed Identify Priority Patients based on Physical Findings Learning Objectives

5. Why Should I Care? • Statistically, for each fatality, there will be four serious injuries and 18 minor injuries. • These collisions cost in excess of one billion dollars annually in the United States alone. • In 2001 in the U.S. there were 45,000 bicyclists injured and 728 killed. • In 2001 in the U.S. there were 78,000 pedestrians injured and 4,882 killed.

6. What are the Dynamics of Trauma? • Dynamics is a branch of Mechanics which is a field of Physics. • The study of Dynamics is concerned with the effects of forces on a body, especially forces that do not originate within that body.

7. The Evolution of Physics • Aristotle • 384-322 B.C. • Greek philosopher and scientist

8. The Evolution of Physics • Galileo • 1564-1642 • Italian physicist and astronomer

9. The Evolution of Physics • Isaac Newton • 1642-1727 • English physicist, mathematician, theologist and alchemist

10. Newton’s First Law of Motion • In the absence of outside forces, an object at rest will remain at rest, and an object in motion at a constant velocity will remain in motion at an unchanged velocity indefinitely.

11. Newton’s Second Law of Motion • When a force is applied to an object, the object is accelerated. This acceleration is in the direction of the force and proportional to its strength, and is also inversely proportional to the mass being moved.

12. Newton’s Third Law of Motion • Forces are always produced in pairs, with opposite directions, and equal magnitudes.

13. Practical Application - Motion • Pedestrian struck by a moving vehicle • Pedestrian partially or fully accelerated (+) to speed of striking vehicle • Pedestrian accelerated (-) by slide, tumble, etc • Vehicle & pedestrian both deformed

14. What is Momentum? • Momentum = Mass X Velocity • An object with either large mass or high velocity has great momentum.

15. Conservation of Momentum • In a collision, the total momentum of the colliding objects before the collision, is equal to the total momentum of the objects after the collision.

16. Practical Application - Momentum Prior to Collision 3,500 lb X 40 mph = 140,000 185 lb X 5 mph = 925 Total = 140,925 After Collision 3,500 lb X 38.15 mph = 133,525 185 lb X 40 mph = 7,400 Total = 140,925

17. Why is Physics Important?

18. The “Poor Bastard Rule” In cases of collisions between a motor vehicle and a pedestrian or bicyclist, the latter shall always lose.

19. Case in Point!

20. Another Case in Point!

21. Speed Kills Speed / Chance of Death 20 mph 5% 30 mph 41% 40 mph 84%

22. Three Phase Collision Model • Carry • Fall • Slide / Tumble

23. The Carry Phase The phase during which: • the pedestrian or bicyclist is in initial contact with the striking vehicle. • the pedestrian or bicyclist is accelerated, or partially accelerated, to the striking vehicle speed. • initial contact injuries occur.

24. The Fall Phase The phase during which: • the pedestrian or bicyclist breaks initial contact with the striking vehicle. • the pedestrian or bicyclist is acted upon by gravity and begins to return to the earth. • (-) acceleration of the striking vehicle usually begins.

25. The Slide / Tumble Phase The phase during which: • the bicyclist or pedestrian is acted upon by subsequently contacted objects or surfaces. • the bicyclist or pedestrian is likely to experience secondary contact with striking vehicle. • Potential for additional injuries is great.

26. Common Striking Vehicle Shapes • Wedge • Pontoon • Blunt

27. Common Collision Classifications • Wrap • Forward Projection • Roof Vault • Fender Vault

28. Wrap • Usually occurs with pontoon shaped vehicles and is not speed dependent. • Pedestrian is bent around leading edge of vehicle and may be projected forward upon vehicle (-) acceleration. • Pedestrian is fully accelerated to the speed of the striking vehicle. • Usually occurs upon direct anterior or posterior strike.

29. Forward Projection • Usually occurs with wedge or pontoon shaped vehicles at speeds of 25 mph, or less, when strike is above center of mass of pedestrian. • May occur with blunt shaped vehicles at any speed. • Pedestrian is fully accelerated to the speed of the striking vehicle and projected forward.

30. Roof Vault • Usually occurs with wedge or pontoon shaped vehicles at speeds greater than 45 mph. • Pedestrian usually makes secondary contact with striking vehicle on upper windshield or points rearward. • Pedestrian is accelerated to only a portion of the striking vehicle speed.

31. Fender Vault • Usually occurs in off-center lateral strikes at speeds of less than 45 mph. • Pedestrian may have secondary contact with hood, A-post, or windshield. • Pedestrian will usually break contact with vehicle on striking side. • Pedestrian is accelerated only to a portion of the striking vehicle speed.

32. Less Common Classifications Somersault • Pedestrian is projected into the air and returns to earth in front of striking vehicle, usually to be struck again. Drag • Usually a result of second / subsequent vehicle strikes or prone / supine pedestrians, and always associated with significant tissue loss.

33. A Good Reason to Stop Drinking

34. Estimating Initial Area of Impact • Look for footwear and other pedestrian related items farthest from the resting point. • Look for “cone of debris” terminating very near area of initial impact.

35. Estimating Striking Speed of Vehicle • Method works well for wedge and pontoon shaped vehicles. • Must determine initial head strike on vehicle. • Accurate in pedestrian collisions.

36. Estimating Striking Speed of Vehicle MPH Head Strike <25 May be present on hood 25-30 Base of windshield or below 30-45 Base to middle of windshield

37. Estimating Striking Speed of Vehicle MPH Head Strike 45-60 Middle to top of windshield 60 Roof >60 Rear window and points rearward

38. Force / Injury Considerations • Always consider multiple (+) (-) accelerations, multiple contact injuries, and multiple striking vehicles. • Always consider massive (+) (-) acceleration forces and associated injuries to the brain, spine, solid organs, aorta, etc.

39. Life Threats - Head to Mid-Femur • Respiratory Insult • Fractures • Spinal / CNS Insult • Solid Organ Injuries • Impaled Objects

40. Extremity Injuries • Fractures • Amputations • De-gloving • Tattooing • Impaled Objects

41. Fractures & Amputations Striking vehicle speeds of 14 mph or greater, and lower extremity loading, expect lower extremity fractures.

42. Fractures & Amputations Striking vehicle speeds of 45 mph or greater expect lower extremity amputations.

43. Newton’s Laws of Motion and the Conservation of Momentum apply to patients in these types of collisions. The higher the initial head strike on the vehicle, the faster it was moving when it struck the patient. Presentation Summary

44. The larger the vehicle, or the faster it is moving when striking the patient, the greater the energy transferred to the patient. Avoid the temptation to be distracted by extremity injuries…it’s head to mid-femur that kills. Presentation Summary

45. Thank You … … and Let’s Be Careful Out There! Questions or Comments?