Extreme Weather and Streetscapes: Engineering Lighting, Signs, and Fixtures to Withstand Nature’s Fury

When planning a city’s streetscape, it is important to consider durability — the last thing a municipality wants is to replace expensive streetscape fixtures after every weather-related event or natural disaster.

From signs to pole lighting, municipal streetscape fixtures are subjected to extreme forces. For example, one fixture may be subjected to winds of up to 160 miles per hour, while the next will be in direct sun exposure for five to ten years, and, depending on location, heavy rain and/or snow.

From 1980 until the end of 2014 alone, there were over 400 weather or climate-related disasters that resulted in $1 billion in damages in the United States. During the same period, the average interval between weather- or climate-related natural disasters declined from 82 to just 19 days.

The weather-related disasters listed above have made building a durable streetscape a necessity for cities and property owners’ budgets rather than an option.

The Difference Between “Weather Resistant” and “Weatherproof”

The term “weatherproof” is bandied about too loosely in our industry when discussing outdoor products. The truth of the matter is that the ability of a fixture to withstand wind, moisture, temperature variance, and UV exposure is based on solid and accurate design decisions that have been made and documented as part of the entire engineering process (specifically the material science process used in the product) and captured in the manufacturer’s quality assurance and quality control programs. In other words, “weatherproof” should only be used as an expression to describe the inherent absence of leak potential from the fixture in which it is manufactured.

Materials, structure, and surface finish all must work together

Three types of design work together to determine the performance of a fixture throughout its lifetime:

• The structural design governs whether a fixture can support and resist the effects of wind loads, ice loads, and the forces of impacts from vehicle collisions or fallen branches.
• The selection of materials used to construct a fixture determines how it will resist rust, pitting, and fatigue over time.
• The surface finish applied to a fixture protects the underlying component from moisture, salt, and the harmful effects of UV light on the material used to manufacture the fixture.

Each of these categories has a body of engineering standards and academic research that supports it. Knowledge of the standards and research helps explain why certain fixtures can fail after only a few years while other types can last for many generations.

Wind Load Design Standards

Wind load calculations are not a generic calculation; because of the great variability of wind pressure, the National Cooperative Highway Research Program determined in their research that wind pressure requirements are very much site-specific; for example, the design wind pressure required to support a street lighting pole in a coastal location like Mobile, Alabama may be almost twice that for a roadside sign located in an area of low wind pressure. It is for this reason that reputable pole and bracket manufacturers engineer their components to verified load tables and not just to a vaguely defined water/ice loading.

Ice, Snow, and Combined Loadings

Wind is not the only threat to a structure. Ice accumulation can create a large dead load on poles, arms, and sign panels, which is one reason the AASHTO loading provisions incorporate ice, wind, and combined (dead plus live) loads in proximity rather than separately. A pole rated only for wind resistance, but not for the additional mass and drag created by ice accumulation, could, after a winter storm, be structurally inadequate. At the same time, it could very easily handle the load of a summer thunderstorm.

Materials Science: Why Metal Selection is More Important Than it Appears

After structural geometry is determined, the next consideration is what material will actually be used to manufacture the fixture. Outdoor weathering has many different effects on the two materials, aluminum and steel, which are typically used to manufacture streetscape fixtures.

Hot Dip Galvanizing of Steel Components

Steel has several advantages: tensile strength and affordability. However, steel also has one significant disadvantage: it is highly susceptible to corrosion when exposed to moisture and oxygen. Therefore, the industry standard for protecting steel from this type of corrosion is hot-dip galvanizing, ASTM A123/A123M. Steel components are submerged in molten zinc to achieve a metal-bonded coating that provides long-term corrosion resistance; the specification sets minimum coating thickness based on material type and steel weight, as well as finish, appearance, and adhesion requirements, to ensure the coating will perform for the intended lifespan.

The thickness of the coating directly correlates with its service life. Therefore, maintenance of hot-dipped galvanized steel in atmospheric environments will be required sooner and more frequently than for coatings with greater thicknesses, provided all other conditions remain constant.

This is why the specification sheets for high-quality street hardware should specify the exact thickness of the protective coating rather than a general statement about durability.

The advantages of aluminum for streetscape fixtures

When aluminum is exposed to air, it rapidly forms a thin oxide layer; the oxide will self-heal when scratched. This is why the corrosion resistance of aluminum is better than that of most metals without any additional corrosion-resistant treatment.

Aluminum is the material of choice for coastal municipalities, decorative lamp posts, and any products that require a lightweight yet durable material due to its natural rust resistance. This natural rust resistance also helps prolong the life of finishes meant to hold their color and gloss outdoors for many years, so there is no need to be concerned about corrosion occurring beneath the finish.

How Powder Coating Plays a Role in Performance

The structural integrity of an item is how it remains upright; however, the finish of an item is what protects the surface and helps maintain the streetscape in a sharp condition, rather than a chalky, faded condition with rust-streaked components. In the streetscape industry, powder coating has become the standard by which all other finishes are evaluated because it has been tested under the actual conditions that cause paint on metal finishes to degrade when exposed to outdoor conditions.

Testing the Resistance of Humidity and Salt Spray

In evaluating powder coatings, the primary tests used to determine their requirements are ASTM D2247 (to measure how long a coating will maintain its integrity when exposed to continuous moisture) and ASTM B117 (to measure resistance to corrosion from saltwater exposure). According to the manufacturer’s specification data sheet, the expectations to be achieved by powder coatings are 1,000 hours in accordance with ASTM D2247 and ASTM B117 (maximum of one-eighth inch of undercutting and no blistering of the powder coating occurs on any coating) as a means to predict how long a coating will last based upon the elements to which it will be exposed to (i.e., moisture from rain, coastal climate, and winter road salt).

UV Damage and Color Retention.

The primary cause of most coatings’ degradation is sun exposure. The UV rays in sunlight degrade polymer chains, causing fading and/or chalking of surfaces. To verify how well the coatings will perform in UV exposure, manufacturers utilize accelerated QUV weatherometer testing. The QUV weatherometer compresses years of sun exposure into a few weeks of output. In the QUV weatherometer, the coated panels are subjected to an 8-hour UV exposure followed by a 4-hour condensation period, with each cycle repeated approximately 1,000 times. The panels are inspected for color and gloss retention every 250 hours of testing. Research on different powder coating formulations demonstrates the degree of variability within a coating’s chemistry: for example, one study found that certain polyester-based coatings (formulations) have a range of 2,200 to 2,500 hours of UV-A accelerated exposure. At this point, they will have lost 50% of their original gloss. Resin chemistry and formulation quality must be key factors in determining your products’ performance, rather than simply stating that your product has been “powder-coated.”

Many manufacturers of premium finishes are taking the performance of their resin formulations to a new level. For instance, you can find references, such as the one in the overview of industrial coatings, that validate the performance difference of super-durable polyester coatings developed using an engineered molecular structure. The result is that super durable polyester coatings resist hydrolysis, or the breakdown due to water, much better than typical polyester coatings, and provide strong weatherability and moisture resistance. The fluoropolymer systems represent the highest level of both color and gloss retention for extreme architectural applications.

The Value of Understanding Engineering for City and Property Owners

The engineering behind product durability and weather-related fixtures is a valuable area of understanding for the total cost of ownership. An outdated wind map/guide used to specify the base pole, a sign made from bare steel and a fixture that has been finished with a low-end product can be visually the same on the day of installation; however, the difference in real performance will show the difference in 1 – 3 years as rusted streaks on the pole, peeling coatings or fixtures with structural failures when exposed to wind driven rain.

As a result, cities and their respective metropolitan areas can protect the investments they have made by asking suppliers direct questions with specific details regarding the design of their products.

Four questions that engineers and specifiers should ask about streetscape product design

• What structural design standard, such as AASHTO LTS-6, governs the pole or sign support, and what wind speed was it designed for at this specific site?
• What is the zinc coating thickness on galvanized steel components, and does it meet or exceed ASTM A123/A123M minimums?
• What accelerated weathering and salt spray test results are available for the powder coat finish, including hours to failure under ASTM B117 and D2247?
• Is the finish a standard polyester, a super durable polyester, or a fluoropolymer system, and how does that choice affect expected color and gloss retention?

Frequently Asked Questions

How long do properly engineered street fixtures last outdoors?

Service life varies by material, coating, and climate. Still, hot-dip galvanized steel and powder-coated aluminum components are commonly specified for 20 to 30-year design lives in municipal applications, provided routine maintenance is performed, and the original specification matches the site’s wind, moisture, and temperature exposure.

H3: Is aluminum or galvanized steel better for coastal or high-salt environments?

Both perform well when properly specified. Aluminum’s natural oxide layer resists corrosion without additional treatment, while hot-dip galvanized steel develops a protective zinc patina that continues to resist salt exposure over time. The right choice often depends on the structural loads involved, since steel typically offers higher strength for taller poles and longer sign arms.

What is the difference between powder coating and traditional paint for outdoor fixtures?

Powder coating is applied as a dry powder and cured under heat to form a continuous, durable film, whereas liquid paint relies on solvents that evaporate as it dries. Powder coatings generally test better under accelerated humidity, salt spray, and UV exposure standards, which is why they have become the standard finish for municipal lighting, signage, and site furnishings.

Why do wind load requirements change from city to city?

Wind design pressures in standards like AASHTO LTS-6 are calculated from site-specific basic wind speed data, which varies significantly by region, elevation, and proximity to coastlines. A pole engineered for an inland location may be undersized for a coastal or high-plains site, which is why structural calculations should always reference local wind speed data rather than a generic national average.

Do extreme weather trends actually affect how streetscape products should be specified?

Yes. As billion-dollar weather disasters have become more frequent nationwide, many municipalities are re-evaluating whether existing infrastructure meets current wind, flood, and ice loading conditions in their specific regions and are specifying updated structural and coating standards accordingly for replacement projects.