IMSA Traffic Signal III cheat sheet

Yellow change interval: Y = t + v / (2a + 2gG), where t is perception-reaction time, v is approach speed, a is deceleration, g is gravity, and G is grade; verify with field conditions.

Red clearance interval: R = (W + L) / v, where W is intersection width to clear, L is vehicle length, and v is approach speed; convert consistent units to seconds.

Confirm each intersection movement has a phase assignment and that the conflict matrix shows no simultaneous incompatible green indications.

Pedestrian walk interval should be at least 7 seconds and long enough for pedestrians to leave the curb; flashing DON'T WALK uses crossing distance divided by walking speed.

Place primary signal faces for each approach so at least one face is visible from the minimum required sight distance; add supplemental faces where geometry obscures them.

Design stop-bar presence detection for each through lane and use setback detection only where dilemma-zone protection or advance warning is intended.

Check support structures, span lengths, attachment heights, and vertical clearance over travel lanes against agency standards and the electrical code.

Review controller cabinet location, service disconnect, grounding electrode, surge protection, and accessible pedestrian push-button landing and reach range.

Verify anchor-bolt template orientation, conduit stub location, and foundation elevation before concrete placement; recheck after the pour and before pole erection.

Conduit runs between pull points should not exceed 360 degrees of total bends; use sweep bends and pull line or tape for cable installation.

Inductive loop saw cuts must be clean, dry, and sealed; twist loop lead-in wires and test inductance and resistance before connecting to the detector.

Check span-wire or mast-arm signal clearance above the roadway and verify guy wires, attachments, and insulators are installed per the approved shop drawings.

Bond metallic cabinets, poles, and controllers to the grounding electrode system; verify ground continuity and separate power and signal conductors where required.

Perform point-to-point wiring checks from cabinet terminals to field devices before energizing; confirm load-switch assignments match the phasing plan.

Inspect service disconnect, cabinet power supply, surge arrestors, and flasher wiring; confirm the conflict monitor is programmed for the installed signal configuration.

Document as-built conduit, cable, detector, and pole locations, and retain test results for loop resistance, insulation resistance, and lamp/LED load checks.

NEMA TS 2 and ATC controller architectures use different rack and communication designs; confirm cabinet, controller, and detector-rack compatibility before replacement.

Actuated operation uses detector calls to extend or recall phases; gap-out occurs when no call remains during the passage time, while max-out ends the phase at its maximum green.

Presence detection holds a continuous call while a vehicle occupies the zone; pulse detection produces a momentary call and is often used for advance or system detectors.

The conflict monitor, or MMU, monitors field signal voltages and places the intersection in flash when it detects conflicting greens, red failure, or other fault conditions.

NTCIP provides standardized object definitions for traffic controllers and field devices; verify version, baud rate, IP addressing, and polling settings during integration.

Communication media include twisted-pair, fiber optic, and cellular; select based on distance, bandwidth, latency, reliability, and agency ownership of infrastructure.

Time-of-day coordination uses a master or local clock to select timing plans; offsets define the green start relative to the coordination reference point.

Detector design must account for queue storage, turning movements, lane width, and pedestrian or bicycle calls; verify detection coverage after construction or resurfacing.

When a signal is in flash, first read the conflict-monitor event log and field wiring status before replacing controller or detection components.

Preventive maintenance includes inspecting cabinet filters, door seals, surge protection, terminal tightness, lamp or LED operation, and detection performance.

A load switch controls the field signal indication; if one color fails while others operate, check the load switch, controller output, and field wiring for that color.

Loop detector faults are diagnosed with inductance and resistance measurements, a loop tester, and inspection of saw-cut sealant and lead-in splices.

Before changing timing, collect volume, delay, and progression data; after implementation, verify splits, offsets, cycle length, and pedestrian timings in the field.

Coordination failures may result from master-clock drift, communication loss, incorrect local/coordination mode, or a controller database mismatch.

Emergency-vehicle preemption and railroad preemption require periodic testing of detectors, emitters, receiver cards, and controller preemption timing.

Maintain an asset inventory and work-order history for controllers, cabinets, detectors, poles, and communication equipment to support fault tracing and budgeting.

MUTCD Part 4 governs traffic-control signal design, operation, and displays; MUTCD Part 6 governs temporary traffic control for work zones.

Flashing red requires a stop before proceeding; flashing yellow requires slowing and proceeding with caution when clear.

Temporary traffic signals in work zones must be coordinated with flaggers, channelizing devices, and signing so drivers receive consistent direction.

Use NEMA TS 2, ATC, and NTCIP standards to specify controller, cabinet, and communication compatibility; verify local amendments and agency supplements.

Electrical work must follow the applicable electrical code, local amendments, utility requirements, and lockout/tagout procedures before servicing energized equipment.

Accessible pedestrian push buttons require a level landing, operable reach range, clear floor space, and orientation toward the crossing they control.

Work-zone layouts must consider taper length, buffer space, clear zone, worker access, and nighttime visibility; inspect devices for proper retroreflectivity.

Personal protective equipment, traffic control supervision, trenching protection, and arc-flash precautions are required during signal construction and maintenance.