Regulatory Signs
Regulatory signs are the must signs of Idaho roads: white rectangles with black legends, plus red-and-white prohibitions. The exam tests whether you can read the rule a sign imposes, the exact place it applies, and the exceptions that let you proceed anyway.
What the sign is telling you
- A white rectangular sign with black text or symbols sets a legal requirement - speed, lane use, turning, parking, or right-of-way.
- A red circle with a diagonal slash means the action is prohibited.
- A red STOP octagon and a YIELD triangle are regulatory signs even though they control flow rather than list a rule.
- Time and day plates (for example 7-9 AM MON-FRI) limit when the rule applies; outside those hours the restriction is not in force.
Core rules
- An Idaho stop requires a full stop at the stop line, then the crosswalk, then the edge of the intersection, in that order, before yielding to traffic and pedestrians.
- Right turn on red is permitted after a complete stop unless a sign prohibits it. Left turn on red in Idaho is permitted only from a one-way street onto another one-way street.
- Default Idaho limits include 35 mph in urban districts, 25 mph in residential districts, and 20 mph in school zones when posted or flashing. Posted limits are maximums for ideal conditions.
- Lane-use signs, such as mandatory turn arrows and center left-turn lanes, are regulatory; entering a straight-only lane and turning from it is a violation.
Worked example
A NO LEFT TURN sign carries a plate reading 4-6 PM, MON-FRI. At 7 PM on Tuesday the restriction is not active, so a left turn is legal if the signal and traffic allow it. At 5 PM on Monday the turn is prohibited regardless of the signal.
Traps
Treating YIELD as an optional stop; rolling through a right turn on red; ignoring the time plate; assuming a green light overrides a NO TURN ON RED sign.