ACTAR Scene Documentation 5 — Questions and Answers
Question 1: What is the significance of documenting the 'area of impact' (AOI) at a crash scene, and which type of evidence is most diagnostic for locating it?
- It establishes the speed limit; best evidence is signage
- It identifies where the primary collision occurred; best evidence is gouge marks, scrape marks, and fluid deposits in the roadway (Correct answer)
- It defines legal jurisdiction; best evidence is lane markings
- It describes post-crash vehicle paths; best evidence is tire friction marks
Correct answer: It identifies where the primary collision occurred; best evidence is gouge marks, scrape marks, and fluid deposits in the roadway
The AOI is where the collision force was exchanged, and physical evidence such as gouges, scrapes, and fluid drops left by undercarriage contact most precisely locates this zone.
Question 2: When using Structure from Motion (SfM) photogrammetry software to create a 3D model, which camera setting is critical to record in the field to improve model accuracy?
- White balance setting
- Focal length and sensor size (or equivalent 35mm focal length) (Correct answer)
- ISO sensitivity only
- Shutter speed
Correct answer: Focal length and sensor size (or equivalent 35mm focal length)
SfM software uses the camera's focal length and sensor dimensions to model lens geometry; inaccurate or unknown values degrade the accuracy of the reconstructed 3D model.
Question 3: In documenting a nighttime crash scene with artificial lighting, why is it important to photograph the scene under both artificial lighting and in the dark (with only headlight simulation)?
- To show how the scene appeared under investigation conditions and to show how a driver would have seen it at the time of the crash (Correct answer)
- To comply with OSHA lighting standards for field documentation
- To allow comparison with daytime photographs taken later
- To demonstrate that the road markings were visible under all conditions
Correct answer: To show how the scene appeared under investigation conditions and to show how a driver would have seen it at the time of the crash
Documenting under both conditions shows investigators how the scene appeared during evidence collection and recreates the visibility conditions experienced by the involved drivers.
Question 4: What is the purpose of a 'scale bar' or 'scale reference' placed in a photograph of crash scene evidence?
- To indicate the direction of north in the image
- To allow the physical size of objects in the photograph to be determined accurately (Correct answer)
- To mark the boundary of the examined evidence
- To identify who collected the evidence
Correct answer: To allow the physical size of objects in the photograph to be determined accurately
A scale bar placed in the same plane as the subject provides a known reference dimension so that the actual size of documented features can be calculated from the photograph.
Question 5: When a roadway has been resurfaced after a crash, how can a reconstructionist document the original pavement condition for the crash date?
- Only contemporary witnesses can describe the pavement; no other documentation is possible
- Obtain pre-crash maintenance records, road inspection reports, prior crash reports, and any photographs taken near the crash date (Correct answer)
- The case cannot proceed without physical pavement evidence
- Use the current pavement condition as a proxy for the original condition
Correct answer: Obtain pre-crash maintenance records, road inspection reports, prior crash reports, and any photographs taken near the crash date
Maintenance logs, inspection records, prior crash reports, and time-stamped photographs from near the crash date can establish the original pavement condition when the surface has since been altered.
Question 6: Which field measurement error most commonly causes significant positional inaccuracies when using the two-reference-point (triangulation) method with a measuring tape?
- Using a fiberglass tape instead of a steel tape
- Tape sag due to not keeping the tape horizontal and taut during long measurements (Correct answer)
- Recording measurements to the nearest foot rather than inch
- Choosing reference points that are less than 50 feet apart
Correct answer: Tape sag due to not keeping the tape horizontal and taut during long measurements
A sagging, non-horizontal tape reads a longer arc length than the true horizontal distance, introducing systematic error that compounds over longer measurements.
Question 7: What standard practice should be followed when the crash scene crosses jurisdictional boundaries (e.g., county or state lines)?
- Only document the portion within the primary jurisdiction
- Coordinate with all relevant agencies, note the jurisdictional boundary in the documentation, and ensure all areas are fully documented (Correct answer)
- Let each jurisdiction document its own portion independently without cross-referencing
- Defer entirely to the agency with the larger jurisdiction
Correct answer: Coordinate with all relevant agencies, note the jurisdictional boundary in the documentation, and ensure all areas are fully documented
Complete documentation requires coordinating across jurisdictions, clearly noting boundary locations, and ensuring no evidence area is omitted due to jurisdictional gaps.
ACTAR Scene Documentation 5
What is the significance of documenting the 'area of impact' (AOI) at a crash scene, and which type of evidence is most diagnostic for locating it?