# Life Cycle Assessment The International Organization of Standardization (ISO) wrote guidelines for life cycle assessment. - Canonical URL: https://pavementinteractive.org/reference-desk/pavement-management/analysis/life-cycle-assessment/ - Last updated: 2026-11-01 The International Organization of Standardization (ISO) wrote guidelines for life cycle assessment. Examining manufacturing and construction processes and making comparisons between material and process options has great promise for encouraging positive environmental impacts. Standardization of this process leads to greater opportunity for data sharing and adds consistency to reports from different people and organizations. The two reference standards used are ISO 14040-2006 and ISO 14044-2006. These standards describe the principals and requirements for writing an LCA. It is important to note that creating an LCA is an iterative process, and the scope may change throughout the data collection phase in order to make sure the original goal is met. ![ISO 14040-2006 Life cycle assessment framework - The four phases of an LCA](https://pavementinteractive.org/wp-content/uploads/2010/06/ISO14040-20061.jpg) *Figure 1.* ISO 14040-2006 Life cycle assessment framework - The four phases of an LCA ## Sustainability and Pavements Sustainability is a system characteristic that reflects the system's capacity to support natural laws and human values. Natural laws refer to nature and the ecosystems that make it up, such as deserts, forests, prairies and coral reefs. Human values cover basic human needs (food and water, safety, participation, freedom) and economic needs, chiefly the wise use of resources. Five working rules follow from this definition: 1. Do not take things out of the earth faster than nature puts them back. 2. Do not produce things faster than nature can break them down and reintegrate them. 3. Do not degrade ecosystems, because human health and prosperity depend on their proper functioning. 4. Seek quality of life for all people, whether through mobility, access, health or employment. 5. Use resources wisely, including money, time, manufactured items and natural resources. For asphalt pavements, several practices address these rules directly: using more recycled material (rules 1, 3 and 5), lowering production energy with [warm mix asphalt](https://pavementinteractive.org/glossary/warm-mix-asphalt-wma/) (rules 1, 2, 4 and 5) and managing stormwater with porous pavements (rules 2, 3, 4 and 5). Quality construction, long-lasting pavement design, and timely preservation and maintenance address all five rules, and they generally have the largest effect on a pavement's overall sustainability. ## LCA Applied to Pavements An LCA summarizes the inputs and outputs of a process or product over its life: the materials, energy, emissions and products it requires or produces. It runs from the gathering of raw materials to the point at which those materials return to the environment, which is why it is described as "cradle to grave." For a pavement, an LCA can be used to estimate quantities such as its carbon footprint or its energy use. The method grew out of studies of factories and packaging plants, which were obvious point sources of environmental releases; one early precursor was a 1969 study comparing the resource use and environmental releases of different beverage containers. For a paving project, typical inputs include crushed [base courses](https://pavementinteractive.org/glossary/base-course/), pavement aggregate and binder, striping, signage, material transport, paving equipment, and future maintenance and rehabilitation. Outputs include air emissions from material production and construction equipment, solid materials removed from the site, and any other environmentally relevant releases. ### System Boundary The system boundary defines what the assessment includes. In principle an LCA can include everything from cradle to grave, but processes far removed from the project contribute little and are usually left out. For example, an asphalt pavement LCA would not normally include the manufacture of the machinery used to build the asphalt plant. A roadway LCA typically includes the project equipment, materials and transportation, plus the primary manufacture of all the materials, fuels and energy used. ### Analysis Period The [analysis period](https://pavementinteractive.org/glossary/analysis-period/) is the length of time over which environmental impacts are counted. For pavements it should cover rehabilitation as well as initial construction; comparisons of pavement alternatives typically use 40 or 50 years so that several rehabilitation cycles are included. A period that is too short misses the inputs from maintenance and rehabilitation, which can be substantial, in the same way that an LCA of a car that counted only its manufacture would miss most of the emissions from its life. The same reasoning applies to the analysis period in [life-cycle cost analysis](https://pavementinteractive.org/reference-desk/pavement-management/analysis/life-cycle-cost-analysis/). ### Typical Findings Pavement LCAs published by about 2010 suggested some rules of thumb for the shares of a pavement's energy use and CO₂ emissions: - Materials production: about 60 to 80 percent. - Transportation associated with construction (mainly trucking): about 10 to 30 percent. - Construction activities at the job site: less than 5 percent. These shares point to materials production as the stage where improvements have the most effect. ### Limitations and Comparisons An LCA can produce precise-looking numbers from data that are incomplete, outdated, irrelevant to the case at hand, or missing. Around 2010, quality data were scarce for asphalt plant emissions, for the effects of practices such as warm mix asphalt, and for raw material use, including water. Assessments should only be compared when they share assumptions, analysis periods and system boundaries. Pavement alternatives being compared should carry the same loading, have equivalent dimensions and serve a similar use, and ideally draw on the same data sets, since reliable data are hard to obtain and different sources make different assumptions. Where the assessment begins can also change the result. For asphalt pavements, a recurring question is whether to count the embodied (feedstock) energy of the [asphalt binder](https://pavementinteractive.org/glossary/asphalt-binder/), which is a petroleum product. Including it favors concrete alternatives and excluding it favors asphalt alternatives, and the two industries take opposing positions. Most LCA tools have already made an assumption on this point, so it is worth checking what a tool includes and excludes. ### Tools and Policy Few LCA tools are specific to roadways. PaLATE is one: it covers materials, transportation and equipment for both initial construction and rehabilitation. Tools of this kind simplify an LCA but also fix its system boundary, which can make newer technologies or construction practices difficult to include. By 2012, LCA had been written into some government policy, including the U.S. federal Environmentally Preferable Purchasing Program and the Energy Independence and Security Act, as well as many European Union laws and regulations. Several state departments of transportation, including Washington and California, had funded research to establish common practices for pavement LCA. The ISO 14040 and ISO 14044 standards set out how an LCA should be carried out (ISO, 2006[^1]). ## Sustainability Rating Systems Rating systems are a second way to measure sustainability. A rating system lists sustainability best practices and assigns points to each; a project earns points for the practices it adopts and may receive a certification based on its total. The best-known example, LEED (Leadership in Energy and Environmental Design), applies to buildings. In 2010, asphalt pavements could earn only about 3 to 8 of its 100 points, mostly for recycled content and porous pavement. A roadway rating system can credit a wider range of pavement practices: quality construction, long-life pavement design and pavement preservation as well as recycled content and porous pavement. Greenroads, which issued the first version of its roadway rating system in January 2010, is an example. ## Sources [^1]: International Organization for Standardization (ISO) (2006). ISO 14040 and ISO 14044. Environmental Management - Life Cycle Assessment - Principles and Framework, 2nd ed. & Requirements and Guidelines, 1st ed. IHS.