The document discusses accident scene investigation techniques using the Cartesian coordinate system to document evidence. It provides examples of how the system was used to analyze vehicle accidents, premises liability cases, and a products liability case. Measurements of vehicles, marks on the road, and witness statements were plotted on diagrams to determine the alignment and circumstances of collisions.

1. Coordinates & Camera Angles ; Don’t take shortcuts with forensics Jay Gallagher

12. What is it?

13. Applying the grid to a roadway

14. In the Field Applying the cartesian coordinate system to a roadway is easy; view the roadsurface as a plane and use a painted marking as the ordinate

15. Adapting the Cartesian system to curved roadways

16. Measuring a curved road in the field Applying the cartesian coordinate system to a curved roadway is handled the same was as on a straight road; view the roadsurface as a plane and use a painted marking as a curved ordinate and measurements are made the same way

17. What you need to get started Measuring devices - Measuring wheels are useful tools, but be careful of using small diameter wheels, because of their notorious inaccuracy. Use a large wheel for longer measurements. Small wheels are fine for short distances. Multiple tape measures and a good oversized clipboard are recommended as are nomograph templates. Sears sells measuring wheels and tapes. The templates and clipboard can be purchased from engineering supply stores.

18. Pictures are worth 1000’s of words Invest in good quality camera equipment and an appropriate bag to carry gear in. In addition to photo equipment, this bag holds 2 100 foot tapes, two 25 foot tapes, a pocket rod, two 50lb scales, a plumb bob, chalk line, an 8mm camcorder, a digital camera, a panorama camera, a GPS device, an inclinometer, level, compass, light meter, marking chalk, bright orange safety vests, and rain gear. Like a Boy Scout, a good accident investigator is always prepared.

19. Playing in Traffic without getting hurt Effective accident scene investigation requires you to actually get in the street and that should only be done with an eye toward safety. Wear appropriate footwear, high visibility clothing and always maintain a lookout for the flow of traffic. Ideally, you would work with a partner, but in situations where that’s not practical, you can accomplish much the same thing by scoping out your accident scene first and then making most of your measurements along the shoulder, only venturing out into traffic when necessary. The photos on the following five pages illustrate how to conduct most of your measurements from the shoulder.

20. Use a large measuring wheel for the longer measurements. Start measuring from a permanent object, which is not likely to change. Above, measurements are initiated from an expansion joint

21. From the expansion joint, measure along the fog line or the EOP to the item you wish to record, such as a skid mark, or a gouge mark. Above, the item is the start of a skid

22. Once you’ve found the item you want to record, measuring from the reference point at the origin, use the smaller wheel to take an abcissal measurement out to it. This would give the start of the skid mark two measurements

23. With the large wheel, continue with your ordinate measurement to the end of the skid mark.

24. At the termination of the skid, use the small wheel to make another abcissal measurement out to the termination of the skids. There will be two measurements for this point also.

26. Jig Set Up

27. Measuring using a jig

28. Measuring into the crush

29. Measuring the crush

30. Recording Crush Data When measuring a vehicle, use the undamaged end as the origin and measure toward the damaged end. In the illustration at left, the front end of the vehicle is used as the reference and the measurements are made toward the rear end. The length and width of the body are recorded, as are the wheelbase, wheel tracks, overhangs and door frames.

31. Photographing the damage Engineer’s rule in photo to show scale and bumper/damage height

32. Additional relevant photographs Measuring impact absorbers from underneath the vehnicle. It’s easier to photo and measure the impact absorber you’re interested in from the opposite side of the vehicle

34. Skid Pad Usage Using a spring/cylinder scale, measure the weight of your skid pad.

35. Proper skid pad technique Using the same scale, pull the sled laterally and record how much force is required. Divide this number by the weight of the skid to determine the coefficient of friction. Be careful NOT to life UP when you drag the sled. Be sure to drag it laterally, back to you.

37. Duhon Accident Scene

38. Trooper’s 1 st version Trooper’s 1 st Version

39. Lineup suggested by evidence Based on physical data, we determined that the alignment was like this at the time of impact. Coincidentally, the claimant was executing a left hand turn from the right lane to reach a median cut-through because she missed her exit off - ramp

40. Gouge Mark missed by Trooper, inside skid mark

41. Undercarriage Measurements Inspection of the undercarriage of the plaintiff vehicle, show that only ONE undercarriage piece made contact with the asphalt

42. Trooper’s second theory Trooper’s Second Version

43. Primary Direction of Force – claimant crush damage

44. Initial claimant vehicle measurements

45. Claimant Crush Damage Measurements

46. Travel of claimant vehicle as suggested by physical evidence

51. Converging yaw marks in grass

53. Mark denoting final resting position in opposing lane.

54. Deformation of wheel, denoting primary direction of force from the side, rather than the rear

56. Undercarriage damage

57. Additional Undercarriage damage photo. This matches up with the width of the gouge mark

58. Undamaged wheel strut

59. Damaged wheel strut

60. White fiberglass rear spoiler

61. Black Plastic door trim

62. Impact alignment suggested by evidence

63. Damage to the front of insured vehicle

69. 7 Disk tiller

70. 7 Disk tiller extended

71. Marker Arm

73. Accident Scene

74. Putting it all together, accident modeling

75. Case Study IV – Deadmen tell no tales (B&N Construction v SAIA)

77. Using damage evidence to determine alignment at impact

83. The insured tractor was traveling 70 mph or 105 ft per second. (70 * 1.467) Based on the projected travel of both vehicles, a 1/10 th of a second delay would put the point of impact at the left rear tire, in a classic T-bone collision. It would not have been survivable. A 1/100 th of a second delay in braking would put the point of impact on the driver’s side door, equally unsurvivable.

85. Night Time Visibility Studies Digital Cameras are excellent for night-time visibility studies. CCD lenses work like the rods and cones of your eyes. There’s no guesswork regarding aperture openings and exposure times. In the photo above, the plaintiff said she stepped into a hole in the grassy part of the median and broke her ankle because she couldn’t see that it wasn’t paved. - Use a tripod - Suppress your flash - Resultant photo will show the actual lighting conditions and areas of shadows - Works best when there’s SOME ambient light

88. Panoramas and other non-standard photographic techniques Digital images can be stitched together to make Virtual Reality panoramas that you can actually use to “place” the jury at the accident scene without ever leaving the court room.. Digital images can also be stitched together to make long continuous shots and are particularly useful when coupled with overhead photography.