Traffic Signal Fundamentals, Standards, and Terminology
What a signal actually does
A traffic signal assigns right-of-way by time, not by vehicle presence. The vocabulary tested at this level includes phase, movement, interval, cycle length, split, offset, coordination, actuation, preemption, and priority. A phase is a controller timing unit that serves one or more compatible movements; a movement is what a driver actually does. Rings and barriers define which phases may run together.
Standards you must name
MUTCD is the national standard for signs, markings, and signal displays; state and local manuals supplement it. NEMA TS-2 and ATC define controller and cabinet architecture. The NEC governs wiring methods. ITE publishes timing and design practices. Warrants 1 through 9 justify installation, but a met warrant is an engineering finding, not an automatic mandate.
Intervals and displays
Green, yellow change, and red clearance are three separate intervals. Yellow is not a clearance interval by itself. MUTCD sets a 3-second minimum yellow, and red clearance is generally limited to 6 seconds. A flashing yellow arrow is permissive; only a green arrow gives protected right-of-way. Pedestrian displays are WALK, flashing DON'T WALK, and solid DON'T WALK.
Traps
Watch for questions that confuse cycle length with split, offset with split, or overlap with phase. "Warrant met means signal required" is false. "Yellow can clear the intersection" is false. "Lagging left is always safer" is false without context.
Worked example
Yellow change interval by the ITE kinematic formula: Y = 1 + V / (2a + 2gG). For 45 mph (66 ft/s) on level grade with a = 10 ft/s squared: Y = 1 + 66/20 = 4.3 seconds, so use 4.3 seconds rather than the 3-second floor.