Signal Operations & Indications
Not publishedof exam
NEMA PhasesRing-BarrierSignal TimingPedestrian IntervalsSignal HeadsPreemption
Cabinet Wiring & Components
Not publishedof exam
Load SwitchesConflict MonitorController TermsElectrical BasicsFlasher Unit
Vehicle Detection
Not publishedof exam
Inductive LoopsVideo DetectionMicrowave RadarPushbuttonsDetector Testing
Installation & Maintenance
Not publishedof exam
Signal SupportsPull BoxesTroubleshootingPreventive Maintenance
Standards & Legal Requirements
Not publishedof exam
MUTCDNECSignal WarrantsLiability
Communications Systems
Not publishedof exam
Fiber OpticCopper InterconnectWirelessEthernet
Safety
Not publishedof exam
LOTOPPEOSHAWork Zone
Quick Facts
- Exam
- IMSA TST-I
- Credential
- Traffic Signal Technician I
- Questions
- 50 multiple-choice
- Time
- 3 hours
- Pass
- 70%
- Format
- Online proctored
- Level
- Entry-level
- Prereq
- Work Zone cert + 1 yr exp
NEMA Phase Numbering
Evens = through, odds = left
2/6: major through1/5: major left4/8: minor through3/7: minor left
Gap Out vs Max Out
Gap Out
- No call within passage time
- Efficient early termination
Max Out
- Hits maximum green cap
- Forced by conflicting demand
Efficient end vs forced end
NEMA Phases & Ring-Barrier
- Phase 2/6
- Major street through movements
- Phase 1/5
- Major street left turns
- Phase 4/8
- Minor street through movements
- Phase 3/7
- Minor street left turns
- Ring
- Phases that time sequentially
- Barrier
- Point both rings cross together
- Concurrent phases
- Different rings, same time
- Phase
- Timed right-of-way, one movement
Signal Cycle Sequence
Green -> Yellow -> All-Red -> Next Green
Green: right of wayYellow: warning endAll-red: clear vehiclesNext: conflicting green
Yellow Change vs All-Red
Yellow Change
- Warns approaching drivers
- 3-6 seconds typical
All-Red / Clearance
- Clears entered vehicles
- Follows yellow, optional
Warn vs clear
Signal Timing Intervals
- Min green
- Shortest allowed green time
- Max green
- Green cap with conflicting call
- Yellow change
- 3-6 sec warning interval
- All-red / red clearance
- Extra clearance after yellow
- Passage time
- Extends green per vehicle detected
- Gap out
- No call within passage time
- Max out
- Forced end at max green
- Cycle length
- 60-180 sec, one full sequence
- Split
- % of cycle per phase
- Dwell/rest
- Holds green, no conflicting call
Leading vs Lagging Left Turn
Leading Left
- Arrow before through green
- Clears queue first
Lagging Left
- Arrow after through green
- Less common sequence
Before vs after through
Pedestrian Signal Intervals
- Walk
- Steady white walking person
- Pedestrian clearance (FDW)
- Flashing upraised hand, finish crossing
- Walking speed
- 3.5 ft/sec MUTCD default
- Pushbutton
- Places pedestrian call, not instant
- Ped recall
- Walk served every cycle
- Mount height
- 7-10 ft above sidewalk
Preemption vs Priority
Preemption
- Immediately overrides timing
- Trains, emergency vehicles
Priority
- Adjusts timing only
- Transit, does not override
Override vs adjust
Signal Heads & Indications
- Vertical head order
- Red top, yellow, green bottom
- Green ball
- Permissive, yield when turning
- Green arrow
- Protected, exclusive movement only
- Flashing red
- Stop, treat as stop sign
- Flashing yellow
- Proceed with caution
- FYA
- Flashing yellow arrow, permissive left
- Backplate
- Cuts sun phantom glare
- Visor/hood
- Shields lens from sunlight
- Min signal faces
- 2 per approach, MUTCD
- Lens size
- 12-inch standard, 11th Edition
Preemption & Priority
- Preemption
- Interrupts timing for train/EMS
- Opticom
- Optical emitter/receiver EMS preemption
- Railroad preemption
- Highest priority, overrides EMS
- Priority
- Adjusts timing, does not override
Conflict Monitor vs MMU
Conflict Monitor
- TS 1 cabinets
- Basic conflict detection
MMU
- TS 2 cabinets
- Broader fault detection, SDLC
Both force flash on fault
Recall Mode Picker
- Main street coordinated phase→Max recall(Times to max every cycle)
- Side street, low volume→Min recall or none(Serves only on call)
- Crosswalk needs guaranteed walk→Pedestrian recall
- No detectors on approach→Recall required for service
Cabinet Components
- Load switch
- Switches AC power per indication
- Flasher unit
- Alternates power for flash mode
- Flash transfer relay
- Switches controller to flasher
- Conflict monitor / MMU
- Detects conflicts, forces flash
- Police panel
- Manual phase/flash control
- GFI/GFCI
- Trips on ~5mA ground fault
- Surge protector
- Shields electronics from spikes
- Circuit breaker
- Opens circuit on overcurrent
- Detector rack
- Houses loop amplifier cards
Controller Operation Terms
- Call/demand
- Request for phase service
- Recall
- Phase placed in demand always
- Max recall
- Forces max green every cycle
- Actuated signal
- Detector input varies timing
- Semi vs full actuated
- Minor-only vs all-approach detectors
- NEMA TS1
- Legacy conflict monitor standard
- NEMA TS2
- MMU + serial bus standard
Electrical Fundamentals
- Ohm's Law
- V = I x R
- Power formula
- P = V x I
- Series resistance
- Sum of all resistors
- Parallel resistance
- Always less than smallest resistor
- Signal voltage
- 120 VAC standard operating
- AC frequency
- 60 Hz in US
- Voltage drop
- IxR loss along cable run
- Megger test
- Checks cable insulation resistance
- Multimeter
- Measures volts, amps, ohms
- 80% continuous rule
- Derate breaker for 24/7 loads
Detection Technology Family
Loop = embedded, video/radar = above ground
Loop: in-pavement wireVideo: camera pixelsRadar: reflected microwavePushbutton: pedestrian call
Loop vs Video Detection
Inductive Loop
- In-pavement wire
- Requires saw cut
Video Detection
- Camera-based, non-intrusive
- Weather/lighting sensitive
Embedded vs above-ground
Detector Selection Picker
- Stop-line, in-pavement detection→Inductive loop(6x6 quadrupole)
- Multi-lane, non-intrusive, cameras ok→Video detection(Weather-sensitive)
- Above-ground, speed + presence→Microwave/radar detector(Non-intrusive)
- Pedestrian crossing demand→Pushbutton(Places a call)
- Insulation resistance test needed→Megger (megohm meter)
Detection Technologies
- Inductive loop
- Senses inductance change, in-pavement
- Video detection
- Analyzes pixel change, non-intrusive
- Microwave/radar
- Reflects signal, speed + presence
- Pedestrian pushbutton
- Detector placing pedestrian call
- Detector amplifier
- Converts loop signal to call
Signal Cable vs Loop Lead-In
Signal/Interconnect Cable
- IMSA Spec 19-1/20-1
- Head + interconnect wiring
Loop Lead-In
- IMSA Spec 50-2
- Shielded twisted pair, detector
Different cable, different job
Loop Detector Details
- 6x6 quadrupole
- Standard stop-line loop shape
- Sensitivity
- Threshold for triggering detection
- Common failure
- Pavement cracks break loop wire
- Loop lead-in
- IMSA Spec 50-2 cable
- Signal/interconnect cable
- IMSA Spec 19-1 or 20-1
Troubleshooting Order
Power -> controller -> load switch -> field -> head
Power: check firstController: logic + timingLoad switch: field powerHead: last check
Dark Signal vs Flash Mode
Dark Signal
- Total power loss
- Treat as all-way stop
Flash Mode
- Intentional or fault-triggered
- Main yellow, side red
No power vs controlled state
Field Troubleshooting Picker
- All signals dark→Check power at cabinet first
- Intersection stuck in flash→Check conflict monitor fault log
- Coordination lost between intersections→Check interconnect + baud settings
- Loop gives false or no calls→Check sensitivity, then megger test
- Signal knocked down by vehicle→Secure scene, add traffic control
Signal Supports & Installation
- Mast arm
- Cantilevered structural signal support
- Span wire
- Cable-suspended signal mounting
- Strain pole
- Anchors span wire tension
- Pull box/handhole
- Underground cable access point
- Drip loop
- Prevents water tracking into equipment
- Head aiming
- Aligns to approaching driver view
- Foundation check
- Verify depth, rebar, conduit stub
Maintenance & Troubleshooting
- Dark signal
- Total power loss, all out
- Troubleshoot order
- Power, controller, load switch, field
- LED maintenance
- Clean lens, check luminance
- Preventive maintenance
- Scheduled inspection before failure
- Knockdown procedure
- Secure, control traffic, document
- Conduit fill
- Max ~40% cross-section filled
MUTCD Statement Hierarchy
Standard shall, Guidance should, Option may
Standard: mandatoryGuidance: recommendedOption: permissiveSupport: informational
MUTCD Essentials
- MUTCD
- Manual on Uniform Traffic Control Devices
- Standard
- Mandatory, uses word 'shall'
- Guidance
- Recommended, uses word 'should'
- Option
- Permissive, uses word 'may'
- Support
- Informational background only
- Part 4
- Highway Traffic Signals section
- 9 signal warrants
- Justify further engineering study
- 11th Edition
- Current MUTCD, effective 2024
NEC & Legal Requirements
- NEC Article 250
- Grounding and bonding rules
- Ground wire color
- Green or green/yellow stripe
- Ground rod max
- 25 ohms resistance or less
- Documentation
- Protects agency from liability
- Prerequisite cert
- IMSA Work Zone Technician required
Communications Media Picker
- Long-haul, high bandwidth corridor→Single-mode fiber
- Short cabinet-to-cabinet link→Copper twisted-pair
- No trenching feasible→Wireless interconnect
- Verify fiber break location→OTDR test
- Devices won't communicate→Match baud rate + address
Communications Media
- Interconnect
- Shares coordination data between controllers
- Single-mode fiber
- Long-haul, high-bandwidth preferred
- Copper twisted-pair
- Short-distance interconnect cable
- Wireless interconnect
- Avoids trenching new cable
- Field master
- Coordinates local controllers, closed-loop
- Baud rate
- Serial data speed, bits/sec
- OTDR
- Locates fiber breaks, measures loss
- Ethernet
- IP comms among cabinet devices
Safety Practices
- LOTO
- Prevents unexpected re-energization
- PPE
- Insulated gloves rated for voltage
- OSHA
- Occupational Safety and Health Administration
- Work zone setup
- First step before any work
- Class C extinguisher
- Rated for electrical fires
- Live wire on cabinet
- Do not touch, call utility
Common Traps
Standard ≠ Guidance
Standard means shall, mandatory ≠ Guidance means should, recommended
Conflict monitor ≠ timing device
Only detects unsafe conflicts ≠ Never sets or counts time
Green ball ≠ green arrow
Ball is permissive, yield turning ≠ Arrow is protected, exclusive
Dark signal ≠ flashing signal
Dark means total power loss ≠ Flash can be intentional or fault
Gap out ≠ max out
Gap out ends early, efficient ≠ Max out forced by max green
Loop lead-in ≠ signal cable
Lead-in is Spec 50-2 ≠ Signal cable is Spec 19-1/20-1
Right turn on red ≠ universal
Varies by state/jurisdiction ≠ No Turn on Red overrides
Preemption ≠ priority
Preemption overrides normal timing ≠ Priority only adjusts timing
Last Minute
- 1.50 questions, 3 hours, 70% pass
- 2.Even phases = through movements
- 3.Odd phases = left turns
- 4.Conflict monitor forces flash mode
- 5.Gap out efficient, max out forced
- 6.Green ball permissive, arrow protected
- 7.Standard = shall, Guidance = should
- 8.Loop = in-pavement, video = camera
- 9.NEC Article 250 = grounding
- 10.LOTO before any cabinet work
- 11.Ground wire green or green/yellow
- 12.Fiber preferred for long-haul comms
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