Traffic Signal Operations and Maintenance
Keeping the system running and proving it
The operations half of this domain is about programs, records, and performance; the maintenance half is about diagnosis and restoring service safely.
Operations: an annual (or agency-specified) preventive maintenance program covering cabinet cleaning and filter change, battery and UPS check, conflict-monitor self-test, loop and detection verification, span wire tension and hardware inspection, pole and foundation inspection, and LED module output. Retiming is triggered by development, changed lane geometry, crash patterns, or measured performance - not by calendar alone. Use performance measures: stops, delay, travel time, progression quality, and ATSPM dashboards built on high-resolution controller data.
Maintenance: preserve evidence. Before power-cycling a controller in flash, pull the conflict-monitor event log. Typical faults are ground faults, failed loops and splices, water intrusion, damaged risers, and loose terminations. Know the MUTCD rules for a signal in flashing mode (red flash means stop, yellow flash means proceed with caution) and for a dark signal, where temporary stop signs and advance warning are typically deployed.
Records matter: asset inventory with GPS, controller and monitor serials, timing sheets, and as-builts. Response times should be defined in writing for knockdowns, dark signals, and flash conditions.
Worked example: a signal goes to flash at 07:40 and the crew arrives at 08:25. The first action is not to reset - it is to read and record the monitor event log, note the fault type, then check the indicated phase and detector before restoring.
Traps: resetting without capturing logs; treating yellow flash as a stop condition; leaving a signal dark without temporary controls; assuming LED modules can be field-repaired.