ACTAR Evidence Documentation & Interpretation 4 — Questions and Answers
Question 1: When preparing a scaled diagram of a crash scene, what is the minimum recommended scale for a diagram submitted in a legal proceeding?
- 1 inch = 100 feet
- A scale that clearly shows all relevant evidence with legible dimensions (Correct answer)
- 1 inch = 10 feet regardless of scene size
- Any scale as long as GPS coordinates are included
Correct answer: A scale that clearly shows all relevant evidence with legible dimensions
The scale should be chosen so that all relevant evidence is clearly visible and dimensions are legible; there is no single mandatory scale, but clarity and accuracy are paramount.
Question 2: Striations (fine parallel lines) found within a tire skid mark are produced by:
- Individual tread elements (ribs or blocks) of the tire contacting the pavement (Correct answer)
- The wheel's rotational speed during locked-wheel braking
- Road aggregate particles cutting into the tire rubber
- The vehicle's suspension oscillation during braking
Correct answer: Individual tread elements (ribs or blocks) of the tire contacting the pavement
The fine parallel striations within a skid mark are created by individual tread ribs or blocks scraping against the pavement surface during the skid.
Question 3: An accelerometer sled test is conducted at a crash scene primarily to determine:
- The posted speed limit accuracy
- The roadway surface's coefficient of friction (drag factor) (Correct answer)
- The vehicle's braking force distribution
- The sight distance available to drivers at the scene
Correct answer: The roadway surface's coefficient of friction (drag factor)
An accelerometer sled test measures the deceleration of a known weight dragged across the pavement, allowing calculation of the surface's drag factor (coefficient of friction).
Question 4: Which photographic documentation technique is specifically used to capture the overall scene context and orient the viewer to the crash environment?
- Close-up (detail) photography
- Macro photography of individual evidence items
- Overall (overview) photography from a distance (Correct answer)
- Comparison photography with a scale ruler
Correct answer: Overall (overview) photography from a distance
Overall or overview photographs are taken from a distance to establish scene context, show the road environment, and orient the viewer before close-up detail is shown.
Question 5: In evidence interpretation, 'contact damage' on a vehicle is distinguished from 'induced damage' in that:
- Contact damage is always more severe than induced damage
- Contact damage is caused directly by the collision force; induced damage results from structural stress transferred through the vehicle (Correct answer)
- Induced damage only occurs in rollover crashes
- Contact damage is limited to the exterior panels of the vehicle
Correct answer: Contact damage is caused directly by the collision force; induced damage results from structural stress transferred through the vehicle
Contact damage occurs at the direct point of impact, while induced damage propagates through the vehicle's structure as a result of those impact forces being transferred.
Question 6: When documenting night visibility conditions relevant to a crash, which measurement is most important to record?
- The moon phase and cloud cover percentage
- The illumination levels (measured in lux) at key scene locations (Correct answer)
- The color temperature of artificial light sources
- The distance between the nearest streetlights
Correct answer: The illumination levels (measured in lux) at key scene locations
Measuring illumination levels in lux at key scene locations (pedestrian position, driver's view point) provides objective, quantifiable data about visibility conditions at the time of the crash.
Question 7: When a crash scene contains evidence of multiple impacts or complex vehicle interactions, the reconstructionist should document the scene in what order?
- From the final rest positions backward toward the point of impact
- Randomly, ensuring all items are eventually photographed
- From the point of first contact forward through the event sequence (Correct answer)
- Only the primary impact area; secondary contacts are not evidentiary
Correct answer: From the point of first contact forward through the event sequence
Documentation should follow the crash sequence from first contact forward, as this logical order helps establish causation and sequence of events in the reconstruction.
ACTAR Evidence Documentation & Interpretation 4
When preparing a scaled diagram of a crash scene, what is the minimum recommended scale for a diagram submitted in a legal proceeding?