Transport emissions are a significant contributor to New Zealand’s greenhouse gas (GHG) emissions.
As shown in the diagram below, the emissions can be divided into:
Each of these sources of emissions are discussed in more detail below.
We are working to reduce GHG emissions across the whole of life and use of transport infrastructure. These sources of emissions are considered when assessing options during the business case process.
Construction emission sources include:
Taken all together, these are often referred to as the embodied emissions (or ‘upfront carbon’) of a piece of infrastructure.
The greatest opportunity to reduce embodied emissions lies in the integrated planning and design of transport infrastructure in an urban form that reduces travel demand and makes best use of the existing network. Where new infrastructure is required, we must build cleverly and efficiently.
We are working towards reducing embodied emissions in our infrastructure through developing and adopting our resource efficiency and waste minimisation strategy, together with use of our sustainability rating tools for high-value projects.
Resource efficiency and waste minimisation
The most significant emission sources in construction are associated with steel, concrete, cement (used in base course as a stabiliser as well as in concrete), processing of aggregates and pavement materials, and the fuel (predominantly diesel) used in construction activities. Emissions embodied in the construction materials are the largest source of emissions – in the order of 65% of construction emissions, therefore the consideration of these emissions is not only important for achieving decarbonisation objectives, but also to ensure efficient resource use that has the potential to improve efficiency and reduce costs.
Construction emissions can be estimated using benchmark data for similar structures, estimates derived from standard designs, or from quantitative bill of materials data. Tools such as the Project Emission Estimation Tool (PEET) are available to assist projects.
Project Emission Estimation Tool
Maintenance and operations (M&O) emissions are from similar sources to construction GHG emissions but are related to the materials and activities required to operate, renew and maintain the infrastructure over its service life. These include:
In general, operational emissions are the smallest component of the whole-of-life GHG emissions associated with the transport infrastructure; however, this is dependent on the type of infrastructure. For example, a road tunnel requires energy for lighting and ventilation that is not required for an open road, which may have only lighting, powered signals or message boards.
For roads, the most significant component of maintenance emissions over the whole-of-life are those associated with pavement renewal activities.
We are working towards reducing our M&O emissions through our resource efficiency and waste minimisation strategy and policy.
Resource efficiency and waste minimisation
Considering the embodied GHG emissions of different pavement and surface materials and replacement cycles over the service life is a key decision to be made during road design. The design and condition of the road pavement may also have a significant impact on emissions from vehicle use, and this should be considered during surface/pavement selection.
Emissions from the vehicles using the land transport system (sometimes called enabled emissions) are the second largest source of GHG emissions in New Zealand.
Vehicle emissions are in direct proportion to fuel use – so for any given vehicle, the amount of fuel used and the resulting emissions, are dependent on the vehicle kilometres travelled (VKT), efficiency of the engine, vehicle load, driving conditions (speed, acceleration/deceleration), and road features (including gradient, surface roughness and texture).
Enabled emissions can be reduced by:
We can calculate how a project or operational change is expected to change vehicle emissions using traffic modelling that estimates the number and type of vehicles using the infrastructure, the vehicle kilometres travelled (VKT) by each vehicle, and the speed they are travelling at. The output from the traffic models must then be combined with vehicle emissions factors, such as those contained within the Vehicle Emissions Prediction Model (VEPM), to determine the effect of the project on GHG emissions.
Vehicle Emissions Prediction Model
Guidance on the application of VEPM emissions rates to traffic data or transport model outputs for the purpose of estimating the change in vehicle greenhouse gas emissions is available in the following report.
While emissions from vehicles are typically measured as grams of carbon dioxide equivalent per kilometre travelled (gCO2e/km for light vehicles by fuel type), the equivalent measure for public transport is the emissions per passenger kilometre travelled (gCO2e/pkm). This is because the emissions associated with operation of a train or bus are apportioned based on the average occupancy. For rail and light rail, the emissions associated with operation of the network may be included in the definition of operational emissions.
End-of-life emissions are those associated with disposing of a piece of infrastructure when an asset has reached the useful life, for example the demolition of a bridge. Given the long service life of transport infrastructure, this occurs relatively rarely, and these activities are usually carried out in conjunction with new construction activity, for example to install a replacement piece of infrastructure.
The guidance and policies that apply to construction activities should be applied to end-of-life deconstruction. For example, the emissions associated with the activity of demolishing a bridge can be estimated and tracked, and our resource efficiency and waste minimisation policy and strategy will direct consideration of resource recovery opportunities. As with construction activities, opportunities to reduce emissions in decommissioning and disposal can contribute to efficient resource use that has the potential to improve efficiency and reduce costs.
Resource efficiency and waste minimisation
End-of-life disposal is often not a major consideration within options assessment, except for occasions where a temporary or short-term piece of infrastructure is required. In these cases, the design process should consider how to re-use the materials or the infrastructure.
The proportion of a project’s whole-of-life emissions contributed during the construction phase depends on the nature of each project and whether the project adds vehicle capacity (and hence increases vehicle emissions) across the network.
For example:
