Final answer:
Stop/Slow retroreflective paddles must be 18 inches wide with 6 inches high letters to ensure visibility and effective traffic control.
Step-by-step explanation:
The question pertains to the specifications for Stop/Slow retroreflective paddles, which are used by crossing guards and road construction crews to control traffic. According to the Manual on Uniform Traffic Control Devices (MUTCD) standards, the paddles must be 18 inches wide, and letters must be 6 inches high. This ensures that the paddles are highly visible, easily understood by drivers, and effective at conveying the proper instructions for traffic control, thus enhancing roadway safety.