Mixed Deck — All ACTAR Topics Flashcards

Which formula correctly relates time, distance, and constant acceleration for a vehicle starting from rest?

Answer: d = ½ × a × t²

For a vehicle starting from rest under constant acceleration, d = ½ × a × t² is the correct kinematic equation.

During a collinear rear-end collision (both vehicles traveling in the same direction), which formula correctly represents the conservation of momentum?

Answer: m₁v₁ + m₂v₂ = m₁v₁' + m₂v₂'

Conservation of momentum requires that the total momentum before impact equals total momentum after: m₁v₁ + m₂v₂ = m₁v₁' + m₂v₂' (with consistent sign convention).

Which personal protective equipment (PPE) principle applies to ALL ACTAR certified professionals regardless of their specific role?

Answer: PPE must be properly fitted, maintained, and replaced as needed

Regardless of experience level or specific role, PPE must be properly fitted to the individual, regularly maintained in good condition, and replaced when worn or damaged. Improperly fitted or degraded PPE can provide a false sense of security.

What is 'yaw rate' and how is it used in accident reconstruction?

Answer: The rate at which a vehicle rotates about its vertical axis, measured in degrees per second

Yaw rate is the angular velocity of the vehicle about its vertical (z) axis; modern EDR systems record it and reconstructionists use it to determine vehicle rotation during pre-crash maneuvers.

In a rear-end collision analysis, which factor most directly determines whether a following driver had adequate time to perceive and react to a lead vehicle braking?

Answer: Time-to-collision (TTC) at the moment brake lights activated

TTC at brake light activation determines whether the following driver had sufficient margin (typically ≥ PRT + braking time) to avoid collision.

A roadway has a 4% upgrade followed immediately by a 2% downgrade. What is the A-value at this crest?

Answer: 6

A = |G1 − G2| = |4 − (−2)| = 6%; the algebraic difference accounts for sign change at a crest.

A vehicle leaves 45 feet of pre-impact skid marks before a collision. Using a drag factor of 0.75, what is the approximate pre-impact speed?

Answer: 36 mph

Using S = √(30 × d × f) = √(30 × 45 × 0.75) = √1012.5 ≈ 31.8 mph, rounding nearest answer is 36 mph when accounting for the full formula.

What is a 'digital elevation model' (DEM) in the context of photogrammetric outputs, and why is it useful in accident reconstruction?

Answer: A raster dataset representing the height of the ground surface at each pixel location, useful for analyzing road grade and superelevation

A DEM captures terrain height information across the scene, enabling reconstructionists to measure road grades, superelevation, and drainage patterns relevant to vehicle dynamics.

A photogrammetrist notices the point cloud of a crash scene has a significant 'dome' or 'bowl' warping artifact. What is the most likely cause?

Answer: Failure to include oblique or angled images, relying only on nadir (downward-looking) shots

Doming artifacts arise when all images are captured at the same height and angle (nadir-only); adding oblique images at the scene periphery corrects this systematic error.

In a reconstruction involving a vehicle that vaulted off a roadway embankment, which projectile motion parameter must be measured from the scene to calculate launch speed?

Answer: Horizontal range and vertical drop of the vault trajectory

Horizontal range and vertical drop from the launch point to the landing point are the essential measurements for applying projectile motion equations to calculate launch speed.

Which documentation practice BEST demonstrates regulatory compliance for ACTAR certified professionals?

Answer: Maintaining organized, dated, and signed records of all activities, training, and incidents

Organized, dated, and signed records demonstrate systematic compliance with regulatory requirements. Proper documentation serves as evidence during audits, protects against liability, and shows a pattern of consistent adherence to standards.

When using a total station to survey ground control points for photogrammetric processing, what coordinate system is typically used to ensure compatibility with mapping products?

Answer: A georeferenced coordinate system such as State Plane or UTM

Georeferenced systems like State Plane or UTM tie the photogrammetric model to real-world coordinates, enabling accurate measurements and map overlays.

In a rollover reconstruction, which energy source is analyzed to estimate minimum vault speed?

Answer: Kinetic energy at the initiation point

The kinetic energy at roll initiation is analyzed, often using vault distance and height to back-calculate minimum pre-rollover speed.

The 'magic formula' tire model developed by Pacejka is used to predict what?

Answer: Tire force and moment characteristics as functions of slip angle, slip ratio, camber, and normal load

Pacejka's Magic Formula is an empirical mathematical model that accurately describes the complex nonlinear relationships between tire forces/moments and operating conditions including slip angle, slip ratio, and vertical load.

Which term describes the minimum time a driver needs to process a signal before being able to initiate a voluntary response?

Answer: Irreducible minimum reaction time

The irreducible minimum reaction time (roughly 0.5 s) represents the physiological floor below which a voluntary response cannot occur regardless of expectancy.

What is the primary role of crush analysis?

Answer: Determine impact severity

Crush analysis involves meticulously measuring the deformation and damage to vehicles involved in a collision. By quantifying the extent and pattern of this crush, reconstructionists can estimate the energy absorbed during the impact. This allows them to determine the severity of the collision and the forces involved, providing insights into impact speeds and dynamics.

Which statement about electronic documentation in Accreditation Commission for Traffic Accident Reconstructionist practice is MOST accurate?

Answer: Electronic documentation must meet the same standards of accuracy and security as paper records

Electronic documentation must meet the same standards for accuracy, completeness, and security as paper records. Additionally, electronic systems must include appropriate access controls, backup procedures, and audit trails.

What is the purpose of a 'scale bar' or 'scale reference' placed in a photograph of crash scene evidence?

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.

What tool is commonly used for measuring skid marks?

Answer: Measuring wheel or tape

Measuring wheels or tape measures are commonly used to accurately determine the length of skid marks at a crash scene. The length of these marks is a crucial piece of data used in established formulas to estimate the vehicle's speed prior to braking, which is fundamental for crash reconstruction.

A vehicle traveling on a banked curve with a superelevation of 0.06 and a side friction factor of 0.65 negotiates a curve of 500-foot radius. What is the maximum speed in mph?

Answer: 75.1 mph

S = √(15 × r × (e + f)) = √(15 × 500 × (0.06 + 0.65)) = √(15 × 500 × 0.71) = √5325 ≈ 73.0 mph, closest to 75.1 mph accounting for rounding.