8.3 Traffic Crash Investigation, Diagramming & State Reporting Requirements

Traffic Crash Investigation, Diagramming & State Reporting Requirements

Traffic crash investigation is a specialized scientific discipline requiring Colorado peace officers to preserve perishable physical evidence, document precise mechanical and environmental factors, reconstruct pre-impact vehicular speeds, and fulfill statutory reporting mandates. Officers must distinguish between civil reporting thresholds and criminal hit-and-run statutes, correctly identify physical roadway evidence, perform fundamental mathematical speed calculations, and execute accurate field sketches using standardized coordinate measurement systems.

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1. Colorado State Accident Reporting Mandates (C.R.S. § 42-4-1606 & Form DR 3447)

Colorado statutory law establishes mandatory reporting requirements for drivers and law enforcement agencies following motor vehicle collisions.

Statutory Reporting Thresholds (C.R.S. § 42-4-1606(1))

A formal law enforcement investigation and written report are statutorily mandated whenever a traffic collision results in any of the following:

1. Injury: Any reported or apparent bodily injury to any person, regardless of severity;
2. Death: The death of any person resulting immediately or within 30 days of the collision; or
3. Property Damage: Total aggregate property damage to all vehicles, public fixtures, or private property to an apparent extent of $1,000 or more.

Form DR 3447 (State of Colorado Traffic Crash Report)

• The DR 3447 is Colorado's standardized motor vehicle crash reporting instrument adopted statewide by the Colorado Department of Revenue and Colorado State Patrol.
• Filing Timelines: Under C.R.S. § 42-4-1606(4), investigating law enforcement agencies must forward completed DR 3447 crash reports to the Department of Revenue within 5 calendar days following the conclusion of the investigation.
• Legal Status and Evidentiary Rules: DR 3447 accident reports are public records accessible under the Colorado Open Records Act (CORA). However, under statutory evidentiary protections, mandatory statements made by drivers to an investigating officer solely for the purpose of completing the mandatory accident report cannot be introduced against the driver in subsequent civil liability trials, though physical measurements, scene diagrams, and officer observations remain fully admissible.

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2. Duty to Stop, Render Aid & Hit-and-Run Penalties (C.R.S. §§ 42-4-1601 to 1603)

Drivers involved in motor vehicle collisions in Colorado have affirmative statutory duties. Failing to fulfill these duties constitutes the crime of "Leaving the Scene of an Accident" (commonly termed Hit-and-Run).

Affirmative Statutory Duties of Drivers

1. Duty to Stop (C.R.S. § 42-4-1601 / 1602): Immediately stop the vehicle at the scene of the crash or as close thereto as possible without obstructing traffic more than necessary.
2. Duty to Give Information (C.R.S. § 42-4-1603): Give their name, address, vehicle registration number, and exhibit their driver's license to any person struck or the driver/occupant of any vehicle collided with.
3. Duty to Render Aid (C.R.S. § 42-4-1603): Render reasonable assistance to any person injured in the collision, including making arrangements for medical transport if apparent or requested.
4. Striking Unattended Vehicle or Property (C.R.S. § 42-4-1604 / 1605): Immediately stop and locate the owner or operator, or securely leave in a conspicuous place a written notice stating the driver's name, address, and registration number, and notify the nearest law enforcement agency without delay.

Statutory Penalty Hierarchy for Hit-and-Run Offenses

┌────────────────────────────────────────────────────────────────────────┐
│                     HIT-AND-RUN STATUTORY PENALTIES                    │
├───────────────────────┬──────────────────────┬─────────────────────────┤
│ Result of Collision   │ Statutory Charge     │ Classification & Range  │
├───────────────────────┼──────────────────────┼─────────────────────────┤
│ Property Damage Only  │ C.R.S. § 42-4-1602   │ Class 2 MTO (10–90 days)│
│ Non-Serious Injury    │ C.R.S. § 42-4-1601(2)│ Class 1 MTO (10d–1 year)│
│ Serious Bodily Injury │ C.R.S. § 42-4-1601(2)│ Class 4 Felony (2–6 yrs)│
│ Death                 │ C.R.S. § 42-4-1601(2)│ Class 3 Felony (4–12 yrs│
└───────────────────────┴──────────────────────┴─────────────────────────┘

• License Revocation: A conviction for leaving the scene involving injury, serious bodily injury, or death mandates the assessment of 12 points and immediate administrative driver license revocation under C.R.S. § 42-2-128.

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3. Physical Evidence Identification at Crash Scenes

Physical evidence on the roadway and vehicles provides objective, incontrovertible data to reconstruct collision sequences, determine points of impact, and calculate pre-braking speeds.

A. Tire Mark Classifications and Characteristics

Skip Skids vs. Gap Skids

• Skip Skids (Intermittent locked braking with gaps < 3 to 5 feet): Occur when a locked wheel bounces over roadway bumps, tar strips, or washboard pavement, briefly becoming airborne. Investigation Rule: Measure the entire length from the beginning of the first skid mark to the end of the last skid mark, including the short skips, as one continuous skid distance.
• Gap Skids (Intermittent locked braking with gaps > 10 to 15 feet): Occur when a driver repeatedly applies, releases, and re-applies the brakes in a panic stop. Investigation Rule: Measure each skid segment separately, calculate the speed scrubbed for each distinct skid mark, and combine them using the combined speed formula.

B. Roadway Debris, Gouges, and Scrapes

• Roadway Gouges and Scratches: Deep metal-into-pavement cuts and gouges occur when structural underbody components (control arms, frame rails, engine cradles) are driven downward into the asphalt by the extreme downward force of maximum collision engagement. Investigative Rule: Gouges are prime physical evidence establishing the exact Area of Impact (AOI).
• Underbody Splatter and Debris Fields:
  • Underbody Splatter: Dirt, rust, dried mud, and road grime dislodged from vehicle wheel wells and chassis at the exact moment of initial shock. Falls almost vertically, marking the AOI.
  • Liquid Splatter and Trailing Fluid: Radiator coolant, oil, and transmission fluid spattered at impact (AOI) followed by liquid run-off trails tracing the post-impact path of the vehicle to its final resting position.
  • Hard Debris vs. Soft Debris: Heavy structural parts (batteries, engine blocks, wheels) travel along the vehicle's pre-impact momentum vector; lightweight debris (broken glass, plastic trim) scatters widely downwind and downstream.

C. Contact Damage vs. Induced Damage

┌────────────────────────────────────────────────────────────────────────┐
│                     VEHICULAR DAMAGE CLASSIFICATION                    │
├──────────────────────────────────┬─────────────────────────────────────┤
│ CONTACT DAMAGE                   │ INDUCED DAMAGE                      │
├──────────────────────────────────┼─────────────────────────────────────┤
│ • Direct physical contact with   │ • Force transmission through vehicle│
│   another vehicle or object      │   structure without direct contact  │
│ • Punctures, scratches, paint    │ • Buckled roof panels, warped trunk │
│   transfers, tire rubber rub     │   lids, rippled fenders, bowed doors│
│ • Imprints of headlights/grilles │ • Glass shattered from frame twist  │
│ • Establishes Angle of Impact &  │ • Demonstrates shock wave & crush   │
│   Direction of Collision Force   │   energy dissipation across body    │
└──────────────────────────────────┴─────────────────────────────────────┘

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4. Speed Calculation Principles & Mathematical Formulas

Accident reconstructionists rely on foundational physical laws (work-energy theorem) to calculate vehicular speed from skid mark measurements and roadway friction.

The Standard Minimum Speed Formula

To calculate the minimum initial speed ($S$) required to produce locked-wheel skid marks of a measured distance ($d$):

$S = \sqrt{30 \cdot d \cdot f \cdot n}$

Where:

• $S$ = Minimum calculated vehicle speed in miles per hour (mph) at the start of locked braking.
• $30$ = Mathematical gravitational constant conversion factor ($2 \cdot g \cdot 1.4667^2$, where $g = 32.2 \text{ ft/s}^2$).
• $d$ = Average skid distance in feet across all locked sliding wheels.
• $f$ = Roadway drag factor / coefficient of friction (dimensionless decimal).
• $n$ = Braking efficiency factor (percentage expressed as a decimal, e.g., 1.00 for all 4 wheels locked, 0.60 for front wheels only).

Typical Roadway Drag Factors ($f$)

Combined Speed Formula

When a vehicle slides across multiple roadway surfaces (e.g., skids on asphalt, leaves road onto gravel, and then impacts a tree with residual velocity $S_{\text{impact}}$), the combined total speed is calculated as:

$S_{\text{total}} = \sqrt{S_1^2 + S_2^2 + S_3^2 + \dots + S_{\text{impact}}^2}$

Critical Curve Speed Formula (Yaw Marks)

To determine the speed of a vehicle sliding laterally in a yaw on a curved path:

$S_{\text{crit}} = \sqrt{15 \cdot R \cdot f}$

Where $R$ is the radius of the circular path determined from chord ($C$) and middle ordinate ($M$) measurements ($R = \frac{C^2}{8M} + \frac{M}{2}$).

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5. Field Sketching, Diagramming & Coordinate Measurement Systems

Precise spatial documentation ensures that a crash scene can be accurately reconstructed in court months or years later.

Essential Elements of a Field Sketch

1. Directional North Arrow (pointing toward magnetic or true North);
2. Roadway geometry (curb lines, lane dividers, fog lines, medians, shoulders);
3. Permanent Reference Points (RPs) (e.g., fire hydrants, utility poles, sewer covers, bridge abutments);
4. Area of Impact (AOI), gouges, scratches, tire marks, and debris fields;
5. Vehicles at their exact Final Rest Positions (FRP) with vehicle headings;
6. Standard disclaimer note: "Field Sketch — Not to Scale".

                               FIELD MEASUREMENT SYSTEMS
        ┌──────────────────────────────────────┬──────────────────────────────────────┐
        ▼                                      ▼
   BASELINE COORDINATE METHOD             TRIANGULATION METHOD
   • Single straight reference line       • Two permanent fixed reference points
   • Measure distance along baseline      • Measure direct straight distance from RP1
   • Measure 90° perpendicular offset     • Measure direct straight distance from RP2
   • Ideal for straight, curbed streets   • Ideal for curves, intersections, open fields

Comparison of Coordinate Measurement Methods

• Baseline Coordinate Method (Station and Offset):
  • Procedure: Establish a fixed Reference Point (RP 0+00) along a straight, continuous roadway edge (e.g., north curb line of Main Street). Measure longitudinal distance along the baseline to a point perpendicular to the evidence item, then measure the exact perpendicular distance at a $90^\circ$ right angle to the evidence point.
  • Application: Highly efficient and accurate for straight streets, highway corridors, and parking lots with straight curb lines.
• Triangulation Coordinate Method:
  • Procedure: Select two permanent, immovable Reference Points (RP1 and RP2) separated by a known, measured baseline distance (e.g., RP1 = Utility Pole #44; RP2 = Northeast Fire Hydrant). Measure the direct straight-line distance from RP1 to the evidence point, and from RP2 to the exact same evidence point. The point is uniquely fixed at the intersection of the two measured radii.
  • Application: Mandatory for curved roadways, complex multi-leg intersections, irregular rural crash scenes, rollover paths off-road, and locations lacking straight reference curbs.