Two drivers say they entered an intersection on green. A photograph taken the following morning shows where the signals hang, but cannot establish which movement had permission to proceed at the time of the collision. Controller records may help resolve the sequence if the intersection recorded and retained useful data.
The investigation has to connect three things: the signal’s actual configuration, the time recorded by its system, and the vehicles’ movements. A list of phase changes is only one part of that work.
Find out what this intersection recorded
The Federal Highway Administration describes systems that log controller inputs and outputs with timestamps, including detector activity and signal-phase changes. Data may be transferred to agency servers or held through a vendor’s service. Those capabilities do not establish that a particular Louisiana intersection has them or that its records still exist.
Identify the road authority responsible for the signal, the intersection or controller number, and any maintenance contractor. Give the crash date, location, approximate time, and directions of travel. Ask who controls the records and whether another agency or vendor retains copies.
A useful request identifies the original event log, the timing plan in effect that day, the phase and detector diagrams, clock information, and relevant maintenance or outage records. Ask about retention promptly and keep the response. Requesting a current timing plan alone may miss an earlier configuration that governed the crash.
Make each record answer a specific question
Scroll horizontally to see all columns. Use the arrow keys when the table is focused.
| Record | Question to resolve |
|---|---|
| Event log and code definitions | What does each entry describe, and is the relevant interval complete? |
| Phase diagram | Which approach, turn, or pedestrian movement corresponds to each phase number? |
| Timing plan and change history | Which configuration was active then, and when was it changed? |
| Detector map and service records | Where was detection occurring, and were faults or repairs documented? |
| Clock, outage, and operating-mode records | Can the timestamps be aligned, and was normal operation interrupted? |
Preserve the original export and its accompanying explanations. A chart made from the data can be helpful, but the underlying entries allow someone else to check the interpretation. Note who supplied the file, when it was exported, and whether any interval or field was omitted.
A phase number must be connected to a movement
A witness may describe a green light without identifying the signal face or lane. Likewise, a controller entry may refer to a numbered phase without naming the driver’s approach. Use the actual intersection diagram and photographs to connect those descriptions.
Distinguish through movements from left turns, arrows, and pedestrian indications. Ask the agency or a qualified traffic engineer what each relevant entry represents. If equipment malfunction is alleged, examine maintenance and physical evidence as well as recorded commands; do not assume one log resolves what a driver could see.
A detector entry also needs context. Before linking it to one of the vehicles, identify the detection area and compare the time with video or other evidence. A sensor response should not be assigned to a particular driver merely because the collision happened nearby.
Align the clocks and test both accounts
Confirm whether each source uses local time or another time standard, whether its clock was synchronized, and whether an offset or interruption is documented. Keep the original timestamps and explain any adjustment in a separate chronology. Changing a time to make it fit a preferred account defeats the purpose of the comparison.
Then compare signal changes with the vehicles’ approach, stop-line entry, turning paths, and impact. Video may show one of those moments but conceal another. Witnesses may have watched different signal faces. State what supports each proposed sequence and where the available timing remains uncertain.
The Baton Rouge intersection guide explains why general crash patterns cannot decide an individual collision. Our discussion of statements and police-report errors addresses conflicting accounts. The intersection-accident practice considers those records alongside signal evidence.
Editorial & Legal Accuracy Notice (Louisiana)
Sources checked: September 30, 2026.
This article provides general information. Available signal records must be interpreted using the actual configuration, timing, and collision evidence.