A Portable Changeable Message Sign (PCM) is considered unacceptable if less than what percentage of pixels per character module are operating properly?

A Portable Changeable Message Sign (PCMS) is crucial for effectively communicating information to drivers, particularly in work zones or during traffic management. For a PCMS to be considered operational and effective, a high percentage of its pixels must be functioning correctly since any significant number of inoperable pixels could severely impair legibility and comprehension of the messages displayed.

When it is stated that a PCMS is considered unacceptable if less than a specific percentage of pixels per character module are operating properly, aiming for 90% functionality ensures that the sign is clear and informative. This threshold is likely established to guarantee that the signs can still convey crucial information to drivers without risking confusion or misinterpretation. If a sign has operational problems beyond this percentage, it may lead to ineffective communication, which could compromise safety and efficiency on the road.

Choosing a lower threshold, such as 80% or 70%, may not provide enough on-screen clarity, and could lead to greater driver distraction or misunderstanding. Similarly, a threshold of 95% is too strict and might be impractical, as it could be challenging to maintain this level consistently under various environmental conditions. Therefore, 90% represents a balanced and reasonable standard for operational effectiveness.