ACTAR Scene Documentation 3 — Questions and Answers
Question 1: When using a Total Station to document a crash scene, what is the purpose of 'backsighting' a known reference point?
- To calibrate the instrument's internal clock
- To establish and verify the instrument's orientation so all measurements are in a consistent coordinate system (Correct answer)
- To measure the height of the instrument above ground
- To confirm battery level before beginning data collection
Correct answer: To establish and verify the instrument's orientation so all measurements are in a consistent coordinate system
Backsighting sets the instrument's horizontal angle reference to a known azimuth, ensuring all subsequent point measurements are oriented in the same coordinate system.
Question 2: Which scale should be placed in a close-up photograph of a small piece of debris or vehicle part at a crash scene?
- A highway mile marker visible in the background
- An ABFO (American Board of Forensic Odontology) scale or ruler placed parallel to the object in the same plane (Correct answer)
- A standard 12-inch ruler held vertically next to the object
- No scale is needed if the object's manufacturer part number is visible
Correct answer: An ABFO (American Board of Forensic Odontology) scale or ruler placed parallel to the object in the same plane
An ABFO or similar flat scale placed in the same plane as the subject allows accurate size determination from the photograph with minimal distortion.
Question 3: In crash scene documentation, what does 'chain of custody' documentation require for physical evidence collected at the scene?
- A list of all witnesses present at the scene
- A continuous record of who collected, handled, transferred, and stored the evidence (Correct answer)
- Photographs taken only by the lead investigator
- Storage in any available container as long as it is labeled
Correct answer: A continuous record of who collected, handled, transferred, and stored the evidence
Chain of custody requires an unbroken documented record of every person who handled the evidence and every transfer, ensuring its integrity and admissibility.
Question 4: What is the recommended lighting condition for overall scene photography when natural light is insufficient?
- Use only the camera's built-in flash to avoid shadows
- Use multiple external light sources positioned to minimize harsh shadows and provide even illumination (Correct answer)
- Avoid photographing in low light and wait until daylight
- Use a single powerful spotlight aimed directly at the scene center
Correct answer: Use multiple external light sources positioned to minimize harsh shadows and provide even illumination
Multiple positioned light sources provide even coverage of large scenes while preventing the deep shadows that a single flash or spotlight would create.
Question 5: When documenting roadway geometry for a crash reconstruction, which measurement is used to define the superelevation (banking) of a curve?
- The radius of the curve centerline
- The cross-slope angle expressed as a rise-over-run ratio across the lane width (Correct answer)
- The posted speed limit through the curve
- The length of the transition spiral into the curve
Correct answer: The cross-slope angle expressed as a rise-over-run ratio across the lane width
Superelevation is measured as the transverse slope (rise per unit of run across the lane), which affects vehicle stability and friction demand through a curve.
Question 6: Which document type is used to formally request and obtain the official roadway design plans from the relevant transportation authority for a crash reconstruction?
- A police incident report supplement
- A public records request or Freedom of Information Act (FOIA) request (Correct answer)
- A deposition notice served on the road agency
- A letter of introduction from the retaining attorney
Correct answer: A public records request or Freedom of Information Act (FOIA) request
Official roadway plans are public records held by transportation agencies and are obtained through a formal FOIA or state-equivalent public records request.
Question 7: What is 'point cloud' data in the context of 3D laser scanning (LiDAR) for crash scene documentation?
- A summary table of GPS coordinates for key scene features
- A dense collection of millions of X, Y, Z coordinate measurements representing the scanned surfaces (Correct answer)
- A digital elevation model averaged across the scene
- Photographs taken from multiple altitudes by a drone
Correct answer: A dense collection of millions of X, Y, Z coordinate measurements representing the scanned surfaces
A point cloud is the raw output of a LiDAR scanner: millions of individual 3D coordinate points that together represent the geometry of all scanned surfaces.
ACTAR Scene Documentation 3
When using a Total Station to document a crash scene, what is the purpose of 'backsighting' a known reference point?