ACTAR Scene Documentation 4 — Questions and Answers
Question 1: When a crash scene has been partially altered before the reconstructionist arrives, what is the most important first step?
- Refuse to document the scene and withdraw from the case
- Document the current condition thoroughly and note specifically what alterations occurred and by whom (Correct answer)
- Recreate the original positions based on witness statements alone
- Measure only the unaltered portions and ignore altered areas
Correct answer: Document the current condition thoroughly and note specifically what alterations occurred and by whom
Documenting the current condition while noting all known alterations preserves what evidence remains and establishes the limits of the reconstruction's evidentiary basis.
Question 2: In crash scene photogrammetry, what are 'control points' and why are they necessary?
- Points where vehicles came to rest, used to estimate final speed
- Surveyed ground points with known coordinates used to scale, orient, and georeference the photogrammetric model (Correct answer)
- Witness positions from which the crash was observed
- Points on the roadway where friction testing is performed
Correct answer: Surveyed ground points with known coordinates used to scale, orient, and georeference the photogrammetric model
Control points with known X, Y, Z coordinates allow photogrammetric software to accurately scale and orient the 3D model to real-world dimensions.
Question 3: What measurement technique is used to locate scene features when a total station or GPS is unavailable and only a measuring tape is at hand?
- Estimation by pacing and converting to feet
- Triangulation using measurements from two or more known fixed reference points (Correct answer)
- Single-offset measurement from the nearest edge of pavement
- Photography only, with scale bars placed at each feature
Correct answer: Triangulation using measurements from two or more known fixed reference points
Triangulation from two known fixed points (such as utility poles or signs) allows accurate location of features using only linear tape measurements.
Question 4: Which statement correctly describes the role of a 'scene diagram' versus a 'scene map' in crash reconstruction documentation?
- They are interchangeable terms with no practical difference
- A scene diagram is a freehand sketch made in the field; a scene map is an accurately scaled drawing prepared from field measurements (Correct answer)
- A scene map is always aerial; a scene diagram is always ground-level
- Scene diagrams are for criminal cases; scene maps are for civil litigation
Correct answer: A scene diagram is a freehand sketch made in the field; a scene map is an accurately scaled drawing prepared from field measurements
A field sketch (diagram) captures rough layout and notes quickly, while a scaled map drawn from precise measurements is the formal product used for analysis.
Question 5: What effect does a camera lens with a wide focal length (e.g., 16 mm) have on crash scene photographs compared to a normal focal length (e.g., 50 mm)?
- It compresses distances, making objects appear closer together
- It exaggerates perspective, making distances between objects appear greater than in reality (Correct answer)
- It produces no perceptible difference in apparent distance
- It reduces depth of field, making background details blurry
Correct answer: It exaggerates perspective, making distances between objects appear greater than in reality
Wide-angle lenses expand apparent depth, causing distances between scene features to look larger than normal human vision perceives, which can be misleading in courtroom presentations.
Question 6: When documenting crash scene evidence in inclement weather, which preservation method is appropriate for protecting perishable tire marks?
- Cover marks with traffic cones spaced 10 feet apart
- Photograph and measure immediately, then cover with plastic sheeting or cones before rain reaches the marks (Correct answer)
- Apply a chemical fixative spray to harden the mark
- Document marks only after weather improves
Correct answer: Photograph and measure immediately, then cover with plastic sheeting or cones before rain reaches the marks
Immediate photography and measurement followed by physical covering preserves the evidence record before rainfall can wash away or obscure tire mark deposits.
Question 7: Which of the following best defines 'oblique photography' as used in crash scene documentation?
- Photography taken from directly overhead (nadir position)
- Photography taken at an angle to the scene rather than vertically, providing perspective views of evidence (Correct answer)
- Photography taken at night using infrared illumination
- Photography using a fisheye lens to capture the full 360° scene
Correct answer: Photography taken at an angle to the scene rather than vertically, providing perspective views of evidence
Oblique photography captures angled perspective views that show the three-dimensional relationships between scene elements, complementing overhead and close-up images.
ACTAR Scene Documentation 4
When a crash scene has been partially altered before the reconstructionist arrives, what is the most important first step?