Toward Sustainable Pavement Systems: A Reference Document
The Federal Highway Administration (FHWA) guide, “Toward Sustainable Pavement Systems: A Reference Document,” synthesizes current knowledge on pavement system sustainability, including the effects that pavement has on climate-related considerations such as stormwater runoff and the urban heat island effect. The guide includes information and extensive synopses of current research on how pavement materials, design, construction, maintenance, and other use considerations can affect and enhance sustainability.
Sustainable pavements are defined as pavements that achieve their intended engineering goals, while preserving and ideally restoring surrounding ecosystems, using resources economically, and meeting basic human needs. The effect of human activities on the environment – including climate change (with a focus on reducing greenhouse gas emission) – is identified as one of the reasons for FHWA's emphasis on sustainability. Separate chapters in the guide describe how to assess and improve the sustainability of pavement systems throughout the entire life cycle:
- Materials (specific materials chosen, as well as production processes including acquisition and processing of materials),
- Design (requirements given site conditions, and pavement structural composition),
- Construction (processes, equipment, and materials involved in constructing pavement systems),
- Use-Phase (influence of pavement on vehicle operations, and interactions between pavement, the environment, and humans),
- Maintenance and Preservation (actions that help slow pavement deterioration), and
- End-of-Life (final disposition and subsequent reuse, processing, or recycling of any portion).
In particular, pavement characteristics such as permeability and albedo can affect pavement sustainability in the context of two key concerns related to climate adaptation: stormwater management and surface temperatures contributing to the urban heat island effect.
Chapter 6, which addresses the use-phase of the pavement lifecycle, includes information on addressing these issues, which ultimately affect human health and water and air quality. Regarding stormwater management, the guide suggests the use of permeable pavements to reduce stormwater runoff, which can help urban areas reduce flooding and water pollution challenges. Conventional pavement surfaces tend to be fairly impermeable, which allows precipitation to run off much faster in heavily developed urban areas than it would in vegetated or undeveloped areas. Additionally, runoff transfers pollutants – including heat – from roadways to stormwater collection systems and waterways, and increases the risk of flooding and erosion during heavy precipitation events. By contrast, permeable pavements can capture runoff and recharge groundwater, therefore reducing the flow of pollutants into waterways while also limiting the need for space-intensive stormwater management systems such as retention ponds. The reference document describes different types of permeable pavements, including porous asphalt, pervious concrete, and permeable paver systems, along with their benefits and drawbacks. For example, research has suggested that porous asphalt is more resistant to freeze-thaw effects than conventional pavements, and therefore may have a longer lifespan in cold climates . However, permeable pavements may be less able to withstand heavy vehicles and high-speed traffic, meaning that the use of permeable pavements may have to be limited to low-volume roadways and parking lots, and roadway shoulders to maximize feasibility and cost-effectiveness.
The guide also describes pavement thermal performance and strategies for reducing urban heat islands. Urban areas tend to have higher surface and near-surface air temperatures than rural areas due to land uses that often involve a much higher concentration of dark and dry surfaces (pavements and rooftops in particular); this is known as the urban heat island effect. Pavements have several thermal properties, most notably albedo (solar reflectance), that influence how they interact with the environment when exposed to sunlight. The interactions are complex and depend on local variables such as building height, shading, and weather patterns. The guide describes these complex relationships and multiple variables that must be considered when designing pavement systems. But in general, pavement with higher albedo absorbs less energy from the sun and reflects more thermal energy, which can contribute to localized cooling and help reduce the urban heat island effect while also improving air quality and human health. Reflective pavements also have implications for water temperature because hot pavements transfer heat to stormwater runoff which then warms receiving waterways; this is a concern particularly for areas that receive significant precipitation during hot seasons. Strategies for reducing pavement heat include using more reflective pavements or special coatings, tree canopy shading to minimize direct sunlight exposure, photocatalytic cements (which accelerate reactions that decompose pollutants, helping to reduce pollution and maintain high reflectivity), vegetated pavers, and adjusting building patterns. For areas near sources of surface water or that experience rainfall during hot seasons, permeable pavements can also help reduce pavement heat even though they are less reflective, because they undergo evaporative cooling that significantly reduces peak surface temperatures.
The guide does not explicitly tie these considerations to climate change adaptation, as most references to climate change in the guide relate to how pavements contribute to emissions and emissions reductions. However, issues such as stormwater runoff and the urban heat island effect may be increasing concerns for many areas depending on their future precipitation and temperature projections, and may also have to be considered in the various lifecycle stages of pavement systems. Another aspect of pavement design not discussed in the guide but relevant to adaptation, includes consideration of how to design pavements to better withstand rapid changes in temperature and thermal expansion and contraction of pavements due to freeze-thaw.
Throughout, the guide emphasizes that sustainable pavements are context-specific and dependent on the relative weighting of agency priorities and the stage of the lifecycle of the pavement system. It also emphasizes that pavements are just one component of the transportation system, and sustainability principles must be applied to the system as a whole rather than to pavements in isolation (Chapter 1).
This Adaptation Clearinghouse entry was prepared with support from the Federal Highway Administration. This entry was last updated on January 28, 2016.
Publication Date: January 2015
- Best practice
- Air temperature
- Heat waves
- Precipitation changes
- Water quality
- Water temperatures