Pavement Temperatures and Effects: Importance of Pavement Temperature
Understanding how pavement temperature affects ice formation and melting is one of the most important factors in effective snow and ice control. Pavement temperature determines whether snow will accumulate on the pavement or melt on contact, whether snow melt or freezing rain may re-freeze or form ice, and help you determine if a deicer is needed and what deicer is appropriate for the conditions. Snow begins to accumulate and ice can form when pavement temperatures fall below 32°F. When pavement temperatures are at or above 32°F, snow can melt on contact even if the air temperature is colder.
Thaw and Refreeze
Winter often brings repeated freeze–thaw cycles. As air temperatures rise above freezing, pavement warms and snow and ice melt, especially on a sunny day. In the evening, pavement may stay above freezing even as air temperatures drop, leaving water on surfaces. When the pavement cools below 32°F, the water refreezes and creates slippery conditions. These freeze–thaw–refreeze cycles repeat throughout the winter, creating hazards that often demand repeated deicer applications.
Factors Affecting Pavement Temperature
Condition | Condition Details | Effect on pavement temperature | Explanation |
|---|---|---|---|
Pavement Type | Asphalt | Warming | Dark color absorbs more sunlight |
Pavement Type | Concrete | Slight warming | Light color absorbs less sunlight |
Weather | Sunny | Warming | Sunlight warms pavement |
Weather | Cloudy | Neutral to slight warming | Lack of or low sunlight |
Weather | Windy | Cooling | Wind can rapidly cool pavement, especially high winds |
Weather | Snow & ice on pavement | Cooling | Snow and ice can cool pavement |
Time of Day | Later morning to afternoon | Warming | Warmer air temperatures and sun warm pavement |
Time of Day | Evening to early morning | Cooling | Cooler air temperatures and lack of sun cool pavement |
Time of year | Mid-winter | Neutral to cooling | Colder air temperature and lower sun angle |
Time of year | Early & Late winter | Warming | Warmer air temperature and higher sun angle |
Subsurface | Early winter | Warming | Warmer soils may prevent/slow pavement heat loss |
Subsurface | Mid-winter | Cooling | Deep frost keeps pavement cold |
Subsurface | Bridges and overpasses | Cooling | No insulation - lose heat faster |
Shade | Shade caused by buildings, trees, hills, objects | Neutral to cooling | Blocks sunlight, deciduous trees let some light through |
Traffic | Heavy traffic | Slight warming | Tire friction, vehicle heat loss, ice breakup, convection can increase temperature |
Expand the dropdowns below to learn more!
Pavement type
Pavement temperature can be measured either within the pavement itself or at the surface. Pavement temperature can vary from the air temperature due to a variety of factors we will discuss in this module including weather, freeze and thaw cycles, shade, and pavement material. Because we remove snow on pavements and apply deicers to surfaces, it is important to understand that your parking lot or sidewalk pavement temperature may be very different than the air temperature at any given time. It may be higher or lower.
Concrete and asphalt are our most common surfaces. Concrete is lighter in color than asphalt so it is likely to be cooler. Concrete and asphalt are our most common pavement types but pavers, pervious pavements, and other surfaces will all vary in pavement temperature. Knowing these differences can influence decisions on the need for deicers and what type of deicer will work best.
These photos show differences in pavement temperature of asphalt and concrete using an infrared temperature sensor. The photos were taken within a few minutes of 11 a.m. The air temperature at the time was 20°F.
Differences in pavement on different surfaces within a few minutes of each other. (Bolton & Menk)
Weather
Wind, sun exposure, snow, humidity, and dew point will have effects on pavement temperature. Wind, especially higher wind speeds, will rapidly cool pavement temperature as much as 5 to 18°F as it passes over the surface. Wind also blows snow across surfaces that can then freeze to the cooled pavement. Surfaces with sun exposure will gradually warm during the day. Darker surfaces will absorb more sunlight leading to significantly warmer pavements, even up to 20°F on dark asphalt pavement. Snow and ice on the pavement can cool the surface, which explains why slippery conditions can occur even when air temperatures are above 32°F. Humidity and dew point affect pavement when warm, moisture-laden air comes into contact with a cooler surface, causing the excess moisture to condense into water droplets on the pavement. With pavement under 32°F, water droplets freeze and create a thin layer of ice, often referred to as black ice because it appears black on asphalt.
Time of day and year
Time of day
When the winter sun is at its highest in the afternoon, it has the greatest impact on pavement temperature due to increased solar exposure and heat absorption. The pavement will remain warm throughout the afternoon, retaining heat before it begins to cool in the evening as the sun sets. Overnight and in the morning when there is the least amount of sunlight, pavements tend to cool. Air temperatures will warm or cool pavement depending on time of day.
Time of year
In the winter, the sun angle is at its lowest on the horizon. With a low sun angle, there are more obstacles to block the sunlight and less direct overhead sunlight to warm the pavement. Additionally, in the winter the days are shorter, meaning less time during the day to provide sunlight onto the pavement. In early winter, the soils beneath the pavement remains above freezing and can slow pavement cooling and even melt light frost or thin ice. Air temperatures will warm or cool pavement depending on time of year.
Subsurface
In winter, the soil beneath pavement becomes very cold and slowly pulls heat out of the pavement. Because the ground warms much more slowly than air, pavement can stay frozen even during sunny days or brief warmups. As winter continues, deep frost keeps pavement cold from the bottom up, meaning surfaces may be below freezing even when air temperatures are above 32°F.
Pavement is usually insulated by the soil beneath it, but elevated surfaces like bridges and overpasses lack this insulation. With cold air above and below, these surfaces lose heat faster and are often the first places where frost or ice forms.
Shade
Shade from trees, hills, objects, and buildings impacts pavement temperature. Shaded areas will have cooler pavement temperatures due to less sunlight reaching the pavement.
It also takes longer, up to about 5 hours, to melt snow and ice on shaded pavement. In the left photo above, ice remains in the shaded area where vehicles are parked. Also notice the scattered shade from the deciduous trees versus the complete shade from the evergreens. In the photo on the right, the sidewalk next to the shops is north-facing and shaded. After plowing or shoveling, it will take longer to melt any remaining snow or ice and is more likely to require use of deicers than in the sunny areas.
The photos below show the difference in asphalt pavement temperature in sun and shade on a sunny day in early March around 11:00 a.m. Photos were taken within 5 minutes of each other. Air temperature was 20°F while the sunny pavement was almost 13 degrees warmer (38.4°F) than the shaded pavement at 25.6°F. Both were higher than air temperature.
Pavement temperatures in sun (left) and shade (right) (Bolton & Menk)
Proximity to heated buildings
Sidewalks and entryways next to heated buildings may have pavement with higher temperatures. In some cases, temperatures may be warm enough that deicers aren’t needed, or less deicer can be used. Since most areas are not near heated buildings make sure to check temperatures away from these areas to determine appropriate deicers and application rates for the property.