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Saturday, Sep 30, 2017

Designing Highways for Climate Change

Designing Highways for Climate Change

Highway 40 damaged during the 2013 Alberta floods

Recent extreme floods and associated infrastructure and environmental damage have demonstrated the need to consider the impact of the changing climate on all our projects. At Associated, during the design and construction of roadways and associated infrastructure, we consider two strategies: adaptation and mitigation.  Adaptation involves applying design criteria that consider the potential impact of climate change and future weather patterns on infrastructure.  Mitigation involves using or reusing materials and applying construction techniques that can reduce greenhouse gas (GHG) emissions over a project’s life.

Adaptation - When considering adaptation strategies, we typically identify what impact changes to the climate could have on all the design components that will be included on a project.  A vulnerability assessment is then undertaken on these components to identify if they are susceptible to climate change and what related design criteria should be reviewed based on the probability and severity of impacts.Our transportation engineers and our climate science and modelling experts work together to identify relevant climate parameters that affect transportation infrastructure, and develop estimates of future values of these parameters to inform our design work. Based on this assessment, further analysis is undertaken to identify the predicted changes to the climate within the project area over the design life of the project.  Climate scenarios are developed for the project area by downscaling Global Climate Models to a local grid.  This provides a future forecast of severe weather events on the project.  A detailed summary of the changes is prepared, together with a recommended change to the values in the design criteria.  The criteria are then updated and submitted to the owner for sign off.  On most road projects, the changes in design criteria are affected by precipitation, although wind can impact sign design, while structures and underground infrastructure may have to consider temperature variations.  Depending on the project and its location, temperature can also have a significant impact on permafrost degradation. The process to identify vulnerable design components and revise the relevant design criteria, generally takes four to six person hours to complete.  

Modifying design criteria can impact client/owner standards and policies, so it is important to get client approval prior to commencing design. Budget can be a limitation. However, when a whole life cost-benefit analysis is undertaken, the marginal capital cost increase of implementing adaptation strategies on a project is very often significantly offset by the cost savings achieved by reducing or eliminating the future cost of repair or replacement due to the severe impacts from severe weather events. The process above allows the cost of adaptation measures to be considered against the risk, so that informed decisions can be made and the available money spent in the appropriate areas. Other factors that need to be considered on rehabilitation projects, particularly with precipitation events, is what happens downstream?  Greater capacity within the project area could cause problems elsewhere.  

Mitigation - Road construction represents approximately 10% of the total GHG emissions produced by the transportation sector, although this value does vary depending on the type of road.  The construction of 1 kilometre of freeway can emit the same tonnage of carbon dioxide as 4 kilometres of provincial highway, 15 kilometres of municipal road, and about 33 kilometres of rural roads.  Although some of this difference is down to the carrying width of each type of roadway, the bulk of the variance is due to structures and road furniture.  On the higher classification of roadways, the choice of materials is critical to limit the GHG emissions on the project.

However, for most of the roads that we design, pavement is the major GHG producer.  The two main factors that need to be considered are the extraction and production of pavement materials and the haulage to site.  Asphalt roadways tend to create less GHG emissions than concrete pavements.  Optimizing earthworks to reduce haul distances and using areas within the site to dispose of unsuitable and excess materials has a significant impact on GHG emissions.

The re-use or recycling of existing materials during construction has a significant benefit to the reduction of our carbon footprint during construction. Energy savings in the processing of new materials and in hauling new materials onto the job site from off-site locations can provide significant cost savings and reduce GHG emisions, thereby providing a very effective mitigation strategy.

As with adaptation techniques, a list is made of the typical construction materials and techniques that are likely to be used on a project and then an evaluation is made to calculate the GHG emissions for each item on the list.  On-line tools are available to do this, but simple spreadsheets are used in most cases, as the calculations tend to be similar on each project, and the focus is on the pavement structure, earthworks balance, and construction techniques associated with them.
 
Mitigation measures for construction can lead to the use of alternate materials, some of which are not included in client standards or policies.  Initial and whole life costs need to be considered in the selection of these alternate materials, but most important of all, the mitigation strategies need to be raised and discussed with the client at an early stage of project development, as there will be capital cost and maintenance implications for the client to consider.
 
About the Authors:
 
Alan Emery has more than 35 years of transportation experience and specializes in the design of highways, roadways, and pathways, and also brings expertise in alternate delivery.
 
Sam King has 19 years of experience in the project management, design, utility coordination, and construction inspection of urban and rural roads, highways, multi-use pathways, intersections, and interchanges.