Climate change has become a global issue affecting the environment and human health. Due to population growth and their increased energy consumption, generation of greenhouse gases (GHG) has increased significantly. The transportation sector was proven to be the fastest growing major contributor to global climate change accounting for 20% of the total GHG emissions in the United Arab Emirates. The goal of this project is to make road projects in the city of Abu Dhabi more sustainable towards the environment. The project aims to estimate the carbon footprint associated with road projects in the city of Abu Dhabi following a comprehensive approach that considers all activities within the life cycle of roads. The objectives of the project are to: (1) conduct an extensive literature review of road construction; carbon footprint emissions from road projects; and review local sustainability initiatives that are related to road transport, (2) calculate the carbon footprint of road construction and operation phases for three road cases in Abu Dhabi city, including development of a framework for carbon footprint calculation of road projects, and (3) delineate sustainability issues in road projects and conduct scenario modeling to evaluate potential mitigation measures of reducing the carbon footprint associated with these projects.
This report is referred to as Technical Report III. It reports on all the tasks of the project, with emphasis on model development and scenario analysis. Although the other two objectives have been covered in previous submissions, the report is considered stand-alone as it provides an updated review of the literature, a description of the developed carbon footprint assessment model, and an updated analysis of the three considered case studies. The report then explains the scenario modeling exercise that was carried on and suggests potential mitigation measures to reduce carbon footprint produced by road projects.
Review of the literature regarding carbon footprint of road projects revealed that road transportation is a major contributor to GHG emissions, and its contribution continues to steadily grow despite the latest development in greener practices, technologies, and policies. To remedy this, a number of mitigation measures have been implemented, which have consistently shown to reduce emission levels. However, countries located in the GCC region have shown particularly high road transport GHG emission output; especially, as GHG emission output is normalized by the road length. The literature also revealed that road projects produce GHG emissions at different stages, but road operation is the single, largest GHG producer throughout a road project’s life-cycle. Nonetheless, road construction and rehabilitation may still offer ways to minimize loss of resources, reduce waste generation, and enable the recycling of materials.
A number of assessment tools capable of estimating carbon footprint from road-related projects have been developed over the past several years. However, some of these tools are meant to be used on a macro-level by helping decision makers assess the carbon footprint of transport policies. Others are focused on assessing emissions produced by either private vehicles, public transit, or freight transportation. Further, other assessment tools may only estimate emissions based on a single project stage (e.g., construction phase). Another limitation of the developed assessment tools is that they are limited in their geographical usefulness and cannot be applied to achieve the objectives of this project. As such a comprehensive model (referred to as RoadCO2) was developed to estimate the carbon footprint of road projects along the road life cycle (i.e.,pre-construction, construction, operation, maintenance, and rehabilitation phases).
RoadCO2 is a web-based model with a database that covers almost all activities that emit GHGs during the road life cycle including those originating from direct or indirect sources. The model follows the conventional Bill of Quantity (BOQ) format for entry of data related to the preconstruction, construction, maintenance and rehabilitation phases. The model can be utilized for planning, screening, sustainability evaluation, and for research purposes. While the model currently uses the IPCC emission factors, it is structured in a way to be able to accommodate local emission factors once available.
The RoadCO2 model was used to estimate GHGs emissions from three road projects located in the Abu Dhabi Emirate. These case studies are: (1) Al Rahba City Internal Roads and services, (2) upgrading of Al Salam Street to an expressway, and (3) widening of the Eastern Corniche Road. Results obtained through the model demonstrate that the operation phase is the main contributor to GHG emissions, with a share of more than 80% of the total due to emissions from vehicles and road lighting. Emissions from the construction of the investigated road cases were found to be 43, 350, and 16 thousand ton CO2 eq, respectively. Of these, road works contributed the most to GHG emissions, followed by stormwater works. Other categories considered in the construction phase contributed almost equal proportion to total GHG emissions, but vary from one project to another.
The relative contribution of material and equipment (including their transport to the sites) to GHG emissions of the studied cases varies. For the case of Al Rahab City, about 30% of the emissions was due to material use while 70% was due to equipment use. For the case of Al Salam Street and the Corniche Road, a higher relative contribution of material to GHG emissions was found (about 80%) as compared to emissions due to the use of equipment. This is mainly due to the high usage of concrete and steel in constructing the tunnel for Al Salam Street case and due to the high contribution of road works as well as the use of concrete for relocating the existed sub-surface network of utilities in the case of the Corniche Road.
In the operation phase, the traffic operating in the 2.18-km section of Al Salam Street project produces over 31,068 ton CO2 eq/year, whereas traffic operating on the road network within Al Rahba City produces about 2,891 ton CO2 eq/year. This significant difference is in line with the major dissimilarities between the two transportation facilities. Emissions from passenger cars dominate in Al Rahba city internal roads, whereas light and heavy vehicles dominate in the case of Al Salam Street. Street lighting was also found to be a major contributor to GHG emissions of Al Salam Street and the Corniche Road case studies. However, both irrigation and sequestration were found to have very low impact on the overall GHG emissions rates.
The estimated annual carbon emissions from Al Salam Street is 46,000 ton CO2 eq while emissions from Al Rahba Roads contribute about 10,000 ton CO2 eq. If one is to consider the effect of road works and the activities of the operation phase excluding those associated with vehicle movement, the emission rates associated with the three case studies conducted in this project expressed in kg CO2 eq/m/yr would be 30 for the case of Al Rahba City, 89.2 for the case of Al Salam Street, and 62.1 for the case of the Eastern Abu Dhabi Corniche Road. These values are in the upper range of those reported for some European countries, due possibly to several factors among which are higher irrigation rates of road-planted trees in the UAE, a lower role of sequestration, and higher emissions from use of concrete made of Portland cement.
Thirteen different scenarios were explored to assess their impact on reducing GHG emissions during the construction and operation phase of road projects. The baseline for the investigated scenario are the three investigated case studies. The explored scenarios either altered the activity data or the emission factor associated with the activity. Results showed that the use of LED lights would have a significant impact on reducing GHG emissions of road projects, followed by the use of 25% solar energy for lighting, followed by almost equal impact of using ground granulated blast furnace slag in concrete mix, complete utilization of TSE for irrigation, and increasing the use of LNG by 25% for LDV. When some of the explored individual scenarios were combined, a significant potential impact could be achieved, with an overall GHG emission reduction of 15 to 40% during the road lifecycle. It was found through scenario analysis that recycling asphalt, recycling aggregate, and reducing water usage for road irrigation do not cause a great potential to reduce GHG emissions for road infrastructure. However, these alternatives may offer other environmental benefits and could save valuable resources.
This report suggests several recommendations for possibly other studies that could build up on the achievements made under this project and could result in better estimation of the emitted GHG during the road life cycle.