Traffic Engineering
When a motor vehicle crash occurs, understanding why it happened requires more than simply assigning fault. A traffic engineer plays a critical role in accident investigation by examining how roadway design, traffic control devices, visibility, and driver expectations may have contributed to the event. Their analysis focuses on whether the transportation system functioned as intended and whether any engineering deficiencies increased crash risk.
Below are the key aspects a traffic engineer evaluates during an accident investigation.
1. One of the first areas a traffic engineer examines is the physical layout of the roadway. This includes:
Lane widths and number of lanes
Shoulder width and condition
Horizontal and vertical curves
Grades (uphill or downhill sections)
Medians and barriers
Intersection configuration
Engineers assess whether the roadway geometry meets applicable design standards (such as AASHTO guidelines) and whether deviations from those standards could have contributed to the crash. Sharp curves, inadequate sight distance, narrow lanes, or confusing intersection layouts may increase the likelihood of driver error.
2. Traffic Control Devices
Traffic control devices guide drivers and set expectations. A traffic engineer evaluates:
Stop signs, yield signs, and regulatory signage
Traffic signals and signal timing
Warning signs (curve, speed, pedestrian, etc.)
Pavement markings (lane lines, arrows, crosswalks)
Temporary traffic control (construction zones)
The engineer determines whether devices were:
Properly placed
Clearly visible
Correctly maintained
Compliant with the Manual on Uniform Traffic Control Devices (MUTCD)
Missing, obscured, faded, or improperly placed signs can mislead drivers and directly contribute to collisions.
3. Sight Distance and Visibility
Adequate visibility is essential for safe driving decisions. Traffic engineers analyze:
Stopping sight distance
Intersection sight distance
Obstructions such as vegetation, buildings, or parked vehicles
Visibility of signs and signals
Lighting conditions (daytime vs. nighttime crashes)
If a driver could not reasonably see another vehicle, pedestrian, traffic signal, or hazard in time to react, the roadway environment itself may be a contributing factor.
4. Speed Environment and Speed Limits
Traffic engineers examine how speed relates to the crash by evaluating:
Posted speed limits
Design speed of the roadway
Operating speeds (what drivers actually travel)
Speed transitions or sudden changes
A mismatch between posted speed limits and roadway design can encourage unsafe speeds. Engineers also consider whether speed-related signage, warnings, or traffic calming measures were adequate for the roadway conditions.
5. Driver Expectancy and Human Factors
A critical concept in traffic engineering is driver expectancy—the idea that drivers behave based on what they reasonably anticipate from the roadway.
Engineers assess whether:
The roadway design was intuitive
Traffic control devices were consistent with nearby roads
Lane drops, merges, or unusual patterns were clearly communicated
Sudden changes violated driver expectations
When roadways behave unexpectedly, even attentive drivers may make errors.
6. Intersection Analysis
Intersections are among the most complex and crash-prone locations. A traffic engineer evaluates:
Intersection type (signalized, stop-controlled, roundabout)
Turn lane design and length
Signal phasing and clearance intervals
Queue lengths and congestion
Conflict points and vehicle paths
Signal timing issues, insufficient turn lanes, or confusing right-of-way assignments can all play a role in crashes.
7. Traffic Volume and Operational Conditions
Understanding how busy a roadway is at the time of the crash is important. Engineers analyze:
Traffic volumes
Peak vs. off-peak conditions
Congestion or queuing
Truck or heavy vehicle presence
High volumes can reduce gaps for turning movements, while congestion may obscure visibility or alter driver behavior.
8. Road Surface and Environmental Conditions
Surface conditions can significantly affect vehicle control. Traffic engineers review:
Pavement condition (ruts, potholes, uneven surfaces)
Skid resistance and friction
Drainage and standing water
Weather conditions (rain, fog, glare)
Poor drainage or worn pavement may increase stopping distances or contribute to loss-of-control crashes.
9. Lighting and Nighttime Conditions
For nighttime crashes, engineers assess:
Street lighting presence and spacing
Light levels at intersections and crossings
Glare from oncoming vehicles or nearby sources
Inadequate lighting can reduce hazard detection and reaction time, particularly for pedestrians and cyclists.
10. Compliance With Standards and Best Practices
A central task of a traffic engineer is determining whether the roadway complied with:
MUTCD requirements
AASHTO design criteria
State and local roadway standards
Accepted engineering practices at the time of design
Non-compliance does not automatically mean negligence, but it may indicate increased risk or the need for additional warnings or mitigation.
11. Crash History and Pattern Analysis
Traffic engineers often review prior crashes at or near the location to identify patterns, such as:
Repeated angle crashes at intersections
Frequent rear-end collisions
Pedestrian or bicycle incidents
Nighttime or wet-weather trends
A history of similar crashes can suggest systemic issues rather than isolated driver error.
Conclusion
At Garrett Forensics, our traffic engineers work closely with attorneys, insurers, and municipalities to identify whether roadway design, signage, signal timing, or visibility issues contributed to a crash. Whether the matter involves a complex intersection collision, pedestrian accident, or alleged roadway defect, Garrett Forensics applies proven methodologies to help determine causation and support informed decision-making.
Their analysis is essential in understanding causation, improving roadway safety, and providing clear, defensible opinions in litigation, insurance claims, and safety reviews.
