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How to Improve Highway Sign Visibility

April 18, 2019

Visibility is the main concern for any sign posted on a highway. Without clear visibility from both a distance and close up, signs are useless. The message must be simple and stand out, as it must not be obscured by trees or other objects. Here are essential points to think about when planning your signs for maximum visibility.

Consequences of Poor Visibility

If a sign is placed to warn drivers of potential upcoming hazards, the consequences of poor visibility can be the difference between life and death. A highway with a slick section, perhaps due to icy conditions, is dangerous enough. But if drivers don’t know when to adjust speed in those areas, they can lose control of their vehicles and crash into a divider or oncoming traffic. Improper placement of signs that don’t give drivers enough time to react is also a cause of accidents.

But poor visibility isn’t just a result of an improperly constructed sign or wrong placement. Elderly drivers with steadily declining vision may also cause accidents if warning signs on highways don’t take them into account. America’s aging population above 65 is expected to keep increasing in the next decade, which is why engineers are currently busy on improving highway sign visibility.

The placement of too many signs in one location, however, can lead to visual clutter, making all of it meaningless even to drivers with superior attention span. Redundancy of signs in a linear fashion does not contribute to this effect and helps alert drivers of what to expect ahead. Glare from excessive reflective light can impair vision too, although signs do not account for much of this problem.

Why Reflectivity Matters

The advent of reflective signs has saved many lives, as this technology has made signs more visible at night. The Federal Highway Administration (FHWA) has established guidelines for maintaining minimum reflectivity. Keep in mind that about a half of all traffic deaths occur at night, according to the FHWA, partly due to drunk driving incidents. Yet only a quarter of all driving occurs after dark. Retroreflection is a form of reflection that redirects light from headlights back to its source. Highway signs are commonly designed with retroreflective sheeting material.

The FHWA measures retroreflection in what is called SI units with a device known as a retroreflectometer. This measurement is useful so that authorities know when it’s time to replace faded signs that lose retroreflective properties. Exposure to the sun over several years causes sheeting materials to lose their shine, due to UV-radiation. Other causes of degradation include moisture, pollutants and vandalism.

Visibility Degradation Over Time

When a sign is installed the date should be marked on it so that inspectors know its expected lifespan. When several signs are needed in an area it’s more cost-effective in the long run to install them at once so that they can all be replaced at the same time. By installing signs in groups it’s easier to plan on inspections all at once. Sending work crews out on multiple missions can run up unnecessary costs.

The more signs degrade, the more they lose retroreflectivity and become less visible at night. That’s why signs must be periodically replaced, as the typical lifespan is five to ten years. Signs must be visually inspected by traffic experts from a moving vehicle to ensure nighttime visibility.


Paying attention to highway sign visibility is a key to reducing accidents. Another core action to make roads safer involves placing signs where they can be easily seen and understood. Contact Zumar at our Arizona, California, and Washington locations to learn more about improving highway sign visibility.

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