ACTAR Scene Documentation 2 — Questions and Answers
Question 1: When documenting skid marks at a crash scene, what is the recommended method for measuring curved skid marks?
- Measure only the chord (straight-line distance from start to end)
- Use a tape along the arc of the mark and record the chord and middle ordinate (Correct answer)
- Estimate the length visually and note in the report
- Photograph only, as curved marks cannot be accurately measured
Correct answer: Use a tape along the arc of the mark and record the chord and middle ordinate
Curved skid marks are measured using the arc length along the tire mark, with the chord and middle ordinate recorded to allow mathematical reconstruction of the radius.
Question 2: Which type of coordinate system is most appropriate for documenting a large-scale crash scene covering multiple city blocks?
- Local arbitrary coordinate system
- GPS-based coordinate system tied to a geodetic datum (Correct answer)
- Polar coordinate system from a single fixed point
- Rectangular coordinate system using the nearest building corner
Correct answer: GPS-based coordinate system tied to a geodetic datum
A GPS-based system tied to a geodetic datum provides scalable, reproducible coordinates suitable for large scenes and integration with GIS or CAD software.
Question 3: What is the primary purpose of establishing a baseline in crash scene survey?
- To provide a reference line from which all other measurements are taken (Correct answer)
- To mark the boundary of the crash scene for law enforcement
- To identify the direction of travel of the involved vehicles
- To record the speed limit of the roadway
Correct answer: To provide a reference line from which all other measurements are taken
A baseline is a known reference line, typically along the roadway edge or centerline, from which perpendicular and along-baseline measurements are made.
Question 4: In aerial or drone photography of a crash scene, what minimum overlap between adjacent photos is recommended to ensure complete photogrammetric coverage?
- 10–20%
- 30–40%
- 60–80% (Correct answer)
- 90–100%
Correct answer: 60–80%
A 60–80% overlap between adjacent images ensures that common points appear in multiple photos, enabling accurate 3D reconstruction through photogrammetry.
Question 5: When photographing gouge marks in pavement at a crash scene, which technique best captures depth and three-dimensional character?
- Overhead photo in full sunlight at noon
- Low-angle side lighting (raking light) with a scale marker (Correct answer)
- Wide-angle lens from standing height
- Infrared photography to enhance contrast
Correct answer: Low-angle side lighting (raking light) with a scale marker
Low-angle raking light creates shadows that reveal depth and texture of gouge marks, while a scale marker allows size determination from the photograph.
Question 6: Which statement correctly describes the difference between 'total station' and 'GPS RTK' for crash scene documentation?
- Total stations work outdoors; GPS RTK is for indoor scenes only
- Total stations provide millimeter accuracy without satellite dependency; GPS RTK requires clear sky view and satellite lock (Correct answer)
- GPS RTK is always more accurate than a total station
- Total stations require two operators while GPS RTK requires none
Correct answer: Total stations provide millimeter accuracy without satellite dependency; GPS RTK requires clear sky view and satellite lock
Total stations achieve sub-millimeter accuracy using optical angle and distance measurement without needing satellite signals, whereas GPS RTK requires open sky and reliable satellite lock.
Question 7: What information should be recorded in the field notes when documenting tire mark evidence at a crash scene?
- Color and brand of the tire only
- Location, length, width, direction, surface condition, and relative position to fixed features (Correct answer)
- Estimated speed based on mark length alone
- Only the starting point of the mark
Correct answer: Location, length, width, direction, surface condition, and relative position to fixed features
Comprehensive tire mark documentation requires recording location, dimensions, orientation, surface condition, and relationship to fixed scene features for accurate reconstruction.
ACTAR Scene Documentation 2
When documenting skid marks at a crash scene, what is the recommended method for measuring curved skid marks?