IMSA Traffic Signal I flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Activity Area

The portion of a temporary traffic control zone where work is performed; it contains the work space, the buffer space, and the traffic space through which road users travel.

Buffer Space

The unoccupied longitudinal and lateral distance separating the traffic space from the work space, providing a recovery area for errant vehicles and typically sized to stopping sight distance.

Taper Length Formula

For speeds of 40 mph or less, taper length L equals width W times speed S; above 40 mph, L equals W times S squared divided by 60.

STOP/SLOW Paddle

Standard flagger device at least 18 inches square with 6-inch retroreflective letters; the red octagon side reads STOP and the orange side reads SLOW.

Excavation Five-Foot Rule

OSHA requires a protective system such as sloping, shoring, or a trench box whenever an excavation reaches 5 feet in depth or deeper.

High-Visibility Apparel Class

ANSI/ISEA 107 Class 2 garment at minimum for daytime roadway work, upgraded to Class 3 for nighttime or high-speed conditions.

Minimum Approach Distance

The closest safe distance to energized lines; for circuits up to 50 kV it is 10 feet, and all downed conductors must be treated as energized.

Yellow Change Interval

The clearance interval computed as reaction time plus approach speed divided by twice deceleration with a grade term; typically 3 to 5 seconds.

Cycle Length

The total time required for one complete sequence of all signal indications, equal to the sum of every green, yellow, and red-clearance interval in the sequence.

Overlap

A signal display that serves two or more phases at the same time, such as a right-turn arrow running concurrently with a compatible through movement.

Nine Signal Warrants

MUTCD Chapter 4C conditions used to justify signal installation, including eight-hour volume, four-hour volume, peak-hour, pedestrian, school, coordinated system, crash experience, and grade crossing warrants.

Pedestrian Change Interval

The flashing DON'T WALK time, calculated as the crossing distance in feet divided by a walking speed of 3.5 feet per second.

Preemption

Transfer of intersection control to a special sequence, such as for an emergency vehicle or a railroad crossing, overriding the normal coordinated timing plan.

Ring-Barrier Diagram

A graphic showing phases arranged in two rings separated by barriers; standard NEMA concurrency pairs are 1-6, 2-5, 3-7, and 4-8.

Overhead Mounting Height

The bottom of an overhead-mounted signal face must be at least 15 feet above the pavement, while post-mounted faces must be at least 7 feet above the pavement.

Backplate

A panel mounted behind a signal face, usually with a retroreflective border, that increases conspicuity of the indications against a cluttered background.

IMSA 19-1 Cable

A commonly specified traffic signal cable of 14 AWG twisted pairs used for signal head and detector homeruns between the controller cabinet and field.

Span Wire Sag

The downward deflection of messenger wire between strain poles, typically about 5 percent of the span, which affects signal head height and aiming.

Ground Resistance Limit

The resistance from a grounding electrode to earth should be 25 ohms or less; if the reading is higher, a second driven rod must be added.

Twelve-Inch Signal Lens

Lens size required for new signal installations where the 85th percentile approach speed exceeds 40 mph; 8-inch lenses are used at lower speeds.

Conflict Monitor Unit

Cabinet device that monitors signal output voltages and forces the intersection into flashing operation when a fault such as conflicting greens is detected.

Vehicle Extension

The passage time added to a green after a vehicle leaves the detector; a gap longer than this value allows the phase to terminate.

Minimum Green

The shortest green time allowed after a call is answered; it should be long enough to clear vehicles queued between the detector and the stop bar.

Offset

The time difference, in seconds, between the start of green at a coordinated intersection and the system reference point; it creates progression along an arterial.

Split

The portion of the cycle length allocated to a phase, including its green, yellow, and red-clearance intervals.

Inductive Loop Detector

A wire loop embedded in pavement; a vehicle passing over it reduces loop inductance, which the detector amplifier senses and reports as a vehicle call.

Soft Recall

A controller setting that services a phase during its green band only when no other phase places a call, preventing that phase from resting in red.

Cabinet Flash Fault

The flashing condition entered when the conflict monitor detects a fault; typically flashing yellow for the mainline and red for the minor street.

Megger Test

An insulation resistance measurement made with the circuit de-energized; megohm-range readings indicate sound insulation, while low readings indicate moisture or damaged cable.

Test Switch

A cabinet control that lets a technician force an individual phase to green, yellow, or red for lamp-out, conflict, and wiring verification.

Open Loop Reading

An infinite or off-scale inductance reading on a loop tester, which indicates a broken loop wire or lead-in rather than a working detector circuit.

As-Built Drawings

Field-corrected plans showing the actual installed locations of poles, signal heads, conduit, detectors, and wiring, kept current after every modification.