Traffic Laws, Accident Investigation, and Speed Calculation

Restriction as to Speed

Drivers must operate vehicles at a careful and prudent speed.
Speed should be reasonable and proper, neither too fast nor too slow.

Maximum Allowable Speed

Speed limits vary based on road type and location in the Philippines.
General speed limits are set by the Land Transportation Office (LTO).

Expressways and Toll Roads

Light vehicles: Maximum $100$ kph.
Buses and trucks: Maximum $80$ kph.

National Roads

Light vehicles: Maximum $80$ kph.
Buses and trucks: Maximum $50$ kph.

Urban Areas

Maximum speed limits range from $40$ kph to $60$ kph.
Limits depend on local regulations and road conditions.

Overtaking Rules and Regulations

Overtaking is generally done on the left side of the vehicle being overtaken.

Proper Overtaking

Involves assessing the situation, signaling intent, and executing the maneuver safely.

Exceptions to Overtaking on the Left

On two-lane one-way roads, overtaking may be permitted on either side.
On four-lane two-way roads, similar exceptions may apply.

Proper Lateral Parking

Refers to parking the vehicle correctly within designated parking spaces.

Right of Way

Def: The legal or customary precedence allowing a vehicle to cross or pass in front of another.

Rules of Right of Way (Sec. 42-44 of RA 4136)

At an intersection, the vehicle on the left yields to the vehicle on the right if both arrive simultaneously.
A vehicle approaching an intersection yields to vehicles already within it or turning left across its path.
Vehicles on a highway in a business or residential district yield to pedestrians in a crosswalk.
Exception: Intersections regulated by a peace officer or traffic signal.

Kinds of Traffic Accidents

1. Non-Motor Vehicle Traffic Accident

Accidents on a traffic way involving persons but not a motor vehicle in motion.
Example: A pedestrian and a cyclist collide on a bike path.

2. Motor Vehicle Non-Traffic Accident

Motor vehicle accident occurring entirely off a traffic way.
Example: An accident in a parking lot.

3. Motor Vehicle Traffic Accident

Motor vehicle accident occurring on a traffic way.
Example: A collision at an intersection.

Classification of Motor Vehicle Traffic Accident According to Key Event

1. Running Off Road

Vehicle falling off the roadside or cliff on mountain roads.

2. Non-Collision on Road

Accidents not involving a collision, such as overturning.

3. Collision on Road

Accidents involving any form of collision.

Causes of Motor Vehicle Traffic Accidents

Accidents result from various circumstances and require thorough investigation.
Determining liability involves identifying how and why the accident occurred.

1. Simultaneous Factors

Road conditions.
Driver’s attitude or behavior.
Weather conditions.

2. Sequential Factors

Speed is greater or less than safe.
Defective vehicle (vehicle malfunction).

3. Operational Factors

Road hazards.
Driver’s non-compliance with traffic laws.

4. Perception Factors

Driver’s inability to react promptly.
Driver’s faulty action to escape collision.

Five Levels of Activity in Accident Investigation

Police are guided by specific stages of investigation.

1. Reporting

Basic data collection to identify vehicles, traffic, persons, property, and planned movements.

2. At-Scene Investigation

Determine how the accident happened using available information.

3. Technical Preparation

Data collection and organization for study and interpretation.

4. Professional Reconstruction

Efforts to determine how the accident happened from available information.

5. Cause Analysis

Final analysis of accident causes for prevention of similar incidents.

Chain of Events of a Traffic Accident

1. Perception of Hazard

Seeing, feeling, or hearing and understanding an unusual condition signaling an impending accident.

2. Encroachment

Movement into another traffic unit's path.
Examples: Crossing a center line or entering an occupied crosswalk.

3. Leaving the Roadway

Moving off the improved portion of the traffic way used for vehicular travel (excluding shoulder).

4. Leaving the Road

Moving off the road and shoulder, potentially into a ditch or over a curb.

5. Initial Contact

The first accidental touching of an object by a traffic unit in motion.
Before this point, there is no force between the objects.

6. Maximum Engagement

Greatest collapse or overlap in a collision.
Forces between the traffic unit and object are highest.

7. Disengagement

Separation of a traffic unit from an object it collided with.
Forces between the objects cease.

8. Stopping

Coming to rest, stabilizing the accident situation.
May occur with or without control.

Definition of Key Event

An event characterizing the manner of occurrence of a motor-vehicle traffic accident.
Only one key event in a traffic accident, regardless of the number of traffic units involved.
Fixes the accident with respect to time, place, and type.

Key Events of Traffic Accident

1. Running Off the Road

2. Non-Collision on the Road

3. Collision on the Road

Classification of Accident According to Severity

1. Property Damage

Accident with no injuries but damage to vehicles or other property.

2. Non-Fatal

Accident resulting in non-fatal injuries to one or more persons.

Injury Types

Fatal Injury: Death within 12 months of the accident.
Serious Visible Injury: Bleeding wound, distorted member, requiring the victim to be carried from the scene.
Minor Visible Injury: Abrasion, bruise, swelling, limping, painful movement.
Non-Visible Injury: Complaint of pain without visible signs or momentary unconsciousness.

Crucial Events

Used instead of key event to characterize what occurs to each traffic unit individually.
Reference to the available path rather than the entire road.

Crucial Events in a Traffic Accident

1. Leaving the Available Path

Not the same as running off the road.

2. Turning Over in the Path Without Collision

3. Other Non-Collision in Path

4. Collision with Non-Traffic Object in or Adjacent to the Path

5. Collision with Other Traffic Unit in the Path, Not Marked Vehicle

The Three Points in Traffic Accident

1. Point of Possible Perception

Place and time when the unusual condition could have been perceived by a normal person.
Comes at or before the point of perception.
Delay in perception occurs between the point of possible perception and actual perception.
Inattention and speed are common contributors to delayed perception.

2. Point of No Escape

Place and time after which the accident cannot be prevented.
Driver or pedestrian can no longer avoid the accident.
Mitigation may still be possible (e.g., slowing down).
Sometimes the point of no escape and point of perception are the same.

3. Point of Impact

Term with varied meanings; generally means collision but also implies the force involved.
Sometimes used synonymously with point of initial contact or maximum engagement.
More specific terms are preferable due to varied meanings.

Technical Aspects of Traffic Accident Investigation

Investigators should be able to make proper sketches and measurements.
Properly photograph the scene to show important facts.
Identify physical evidence in hit-and-run cases.
Record facts correctly and determine what happened to help the prosecutor.

Definition of Attributes

An attribute is any inherent characteristic of a traffic way, vehicle, or person affecting the probability of a traffic accident.

Purposes of Traffic Accident Investigation

1. Curiosity about Causes and Circumstances

2. Determining Law Violation

Police seek evidence of law violation to take enforcement action.

3. Insurance Claims Adjustment

Insurance agencies determine negligence to properly adjust damage claims.

4. Accident Prevention

Government officials and authorities gather information to prevent future accidents.

Basic Steps in Traffic Accident Investigation

1. Go to the Scene Quickly

2. Park Correctly

Avoid further collision and facilitate traffic flow.

3. Assess the Situation

Call for necessary assistance.

4. Care for Injured

Protect their personal property.

5. Protect the Scene

Prevent additional collisions.

6. Locate Drivers

Establish identities.

7. Interview Drivers, Participants, and Witnesses

8. Note and Record Physical Conditions

Locations of vehicles and evidence.

9. Take Photographs

When possible.

10. Test and Inspect Vehicles

When applicable.

11. Arrest or Cite Violators

When applicable.

12. Have the Scene Cleared Up

13. Follow-Up at the Hospital

14. Notify Relatives and Survivors

15. Prepare Reports

Hit-and-Run Investigation Considerations

The fleeing driver is not necessarily responsible for the accident.
Reasons for flight are often more important than evading responsibility.
Suspects may report damage as a result of another hit-and-run.

Elements of Hit and Run

1. Prove the Suspect Was Driving a Motor Vehicle

2. The Suspect Was Involved in an Accident

Resulting in death, personal injury, or property damage.

3. Suspect Failed to Stop

Didn't give aid or information when asked by law enforcement.

4. The Suspect Had Knowledge of the Accident

Searching the Scene of a Hit-and-Run Accident

Secure the Scene

Ensure safety, use barriers, and divert traffic.

Document the Scene

Take photos and videos from multiple angles.

Search for Witnesses

Interview bystanders and gather their statements.

Collect Physical Evidence

Vehicle parts, glass, paint, and personal belongings.

Look for Surveillance Cameras

Check nearby cameras for footage.

Search for Vehicle Debris

Fragments from the vehicle.

Check Nearby Businesses

Inquire about suspicious vehicles.

Coordinate with Law Enforcement

Provide collected information and evidence.

Utilize Social Media and Public Appeals

Share information to seek public assistance.

Evidence Collection in Hit-and-Run Cases

Collect unexplained materials from the scene.
Broken parts are more important than damaged parts.
Matching broken parts to the suspect vehicle provides positive identification.

Proving Driving

In all traffic offenses, it must be proven that the accused was driving.
Can be done through eyewitnesses or physical evidence.
Do not assume the owner was driving.

Nature of Common Hit & Run Cases

1. Run Over of Pedestrian on Roadway or Crosswalk

2. Sideswiped of Pedestrian on Sidewalk or Road Shoulders

3. Collision with Moving Vehicle While Overtaking (Same Direction)

4. Collision with Moving Vehicle While Overtaking (Opposite Direction)

5. Damaged Parked Vehicle Along Roadside and Parking Areas

6. Crushed Police Road Blocks

7. Bumping Stray Animal on the Roadway

Technical Preparation (Delayed Traffic Accident)

Data collection and organization for study and interpretation.
Includes measurements, photos, maps, speed estimates, and damage matching.
Third level of traffic accident investigation.

Skid Marks as a Tool in Traffic Accident Investigation

Skid marks occur when brakes are applied suddenly, locking the wheels.
The friction between the brake shoe and drum exceeds the friction between the tire and road.
Valuable for understanding the dynamics of a traffic incident.

Kinds of Skid Marks

1. Made by a Car Going Straight Ahead

Tires lock up and slide in a straight line.
Commonly results from forceful braking.
Appear as long, continuous streaks.
Indicate speed, braking force, and road conditions.

2. Made by a Car Going Sideways

Vehicle loses control and slides or rotates.
Observed in oversteering, understeering, or loss of control during turns.
Exhibit curved or irregular patterns.
Provide clues about vehicle's movement, angle, and steering inputs.

Factors Affecting Speed Calculation from Skid Marks

Calculated speed is always less than the actual speed.

Reasons

Skid marks appear only after tires get hot enough to smear rubber.
Total skid distance cannot be seen because the car hits something.
Braking occurs before skid marks appear.
Brakes are not applied hard enough to lock the wheels.

Reliability of Skid Marks

Most reliable in accidents with pedestrians.
In collision accidents, the amount of damage must be considered.

Scuff Mark

Physical traces left by tires in motion.
Provide forensic evidence for determining the sequence of events.

Types of Scuff Marks

1. Acceleration Scuff Marks

Occur during rapid acceleration.
Tires slip and create friction.
Appear as short, irregular streaks.

2. Yaw Marks

Caused by tires rotating and slipping during sudden changes in direction.
Exhibit curved or swerving patterns.
Indicate speed, angle, and vehicle dynamics.

3. Flat Tire Marks

Occur when a tire loses air pressure.
Appear as wide, flat streaks with less defined edges.
Indicate tire blowouts or punctures.

Skip Skid

Intermittent or discontinuous skid marks.
Characterized by periodic breaks along their length.

Gap Skid

Discontinuous skid marks with gaps between segments.
Provide information about collision dynamics and events.

Flip

Vehicle overturning onto its side, roof, or rolling over.

Types

Side flips.
Roof flips.
Complete rollovers.

Length of a Vehicle and Collision Dynamics

Longer vehicles have greater mass and momentum.
Can result in more force during impact.
Affects stability and maneuverability.
Higher center of gravity increases the risk of tipping.

Skid Marks and Vehicle Length

Longer vehicles generally require more distance to stop.
Skid marks may be longer for longer vehicles.
Wheelbase affects the appearance of skid marks.

Grade or Slope

Incline or decline of a surface.
Measured as the ratio of vertical rise or fall to horizontal distance.
Affects braking, acceleration, and stability.

Braking Performance and Grade

Downhill slopes increase speed, requiring more braking force.
Uphill slopes decrease speed, reducing braking needs.
Steeper grades require longer braking distances.

Skid Marks and Grade

Downhill slopes may result in shorter skid marks.
Uphill slopes may result in longer skid marks.
Slope affects the shape and direction of skid marks.

Calculation of Speed from Skid Marks

Uses the skid-to-stop formula.
$V = \sqrt{\frac{2gd}{f}}$
- Where:
- V = Initial speed of the vehicle (in meters per second, m/s)
- g = Gravitational acceleration (approximately 9.8 m/s^2)
- d = Length of the skid marks (in meters, m)
- f = Coefficient of friction between the tires and the road surface

Example 1

Vehicle leaves 30-meter skid marks on a dry road (f = 0.7).
$V = \sqrt{\frac{2 \cdot 9.8 \cdot 30}{0.7}}$
$V = \sqrt{\frac{588}{0.7}}$
$V = \sqrt{840}$
$V = 28.98$ m/s

Example 2

Vehicle going downhill with a slope of 0.15 and a drag factor of $0.70$ ,
leaves a skid marks of $20.6$ meters.

$SPEED = 15.9 \sqrt{20.6 X (0.70 - 0.15)}$
The vehicle is going down hill, so the grade is negative and is subtracted.

$SPEED = 15.9 \sqrt{20.6 X 0.55}$
$= 15.9 \sqrt{ 11.33}$

The nearest whole number whose square is closest to
11.33 is 3 (3 X 3 = 9).

$11.33/3 = 3.78$

$3.78 +3 = 6.78/2 = 3.39$

$SPEED = 15.9 X 3.39 = 53.90 km/hr$

All calculations are resolved in favor of the driver,

$SPEED = 54 km/hr$

Factor in Accident Analysis

Any circumstance contributing to a result.
Necessary but not sufficient element.
Operational and conditional factors.

Operational Factor

Functional failure of the highway transportation system.
Malfunctions or failures in perception, decisions, or performance.

Sequential Factor

Factors present at the same time that contribute to the cause of an accident.
Generally operational factors.

Simultaneous Factor

Factors present at the same time that contribute to the cause of an accident.
Generally condition factors.

Drag Factors

Represents acceleration or deceleration of a vehicle.
Expressed as a decimal fraction of gravitational acceleration.
When a vehicle slides with locked wheels, the coefficient of friction and drag factor are equal.