Data methodology

Currency and conversion

All financial amounts are reported in Australian dollars unless otherwise stated. Figures in USD may have been converted to AUD using the exchange rate at 30 June 2016 (1 AUD: 0.7426 USD).

GHG emissions

Transurban uses The Greenhouse Gas Protocol: A Corporate Accounting and Reporting Standard (Revised Edition) to draw boundaries around emission sources when quantifying our Scope 1, Scope 2 and Scope 3 GHG emissions. Emission factors and calculation methodologies outlined in the Australian Government Department of Climate Change - National Greenhouse Accounts (NGA) Factors August 2015 are then applied to each data source.

For our USA operations, we calculate Scope 1 GHG emissions using emission factors and calculation methodologies outlined by the United States Environmental Protection Agency (EPA) for the calculation of GHG emissions from transportation and mobile sources.

The EPA’s eGRID2012 tenth edition with 2012 data (released August 2015) is used to calculate Scope 2 and 3 GHG emissions from electricity in the USA.

Transurban applies the GHG Protocol’s air travel method and emission factors to individual flight details to generate our Scope 3 emissions associated with corporate air travel.

Australian Government NGA Factors August 2015 have been used to calculate Transurban’s Scope 3 emissions from waste, fuel use (for incident response and operations and maintenance vehicles), fuel refining and transport and electricity transmission and distribution losses.

Customer travel

GHG emissions from our roadways were calculated using Transurban’s traffic model (developed by Transurban). The model uses traffic data that is extracted from our tolling system and represents actual trips along the roadway. The tolling system records information such as vehicle class and entry and exit points of vehicles, giving an accurate representation of vehicle types and trip lengths. Supplementary information on some assets includes vehicle origin-destination studies for typical travel routes, independent travel time studies, and assumptions based on the physical dimensions of assets. These data are used to calculate the total Vehicle Kilometres Travelled (VKT) on each asset for the year.

Travel speeds are an additional contributing factor in calculating GHG emissions. Our tolling systems on some of these roads time stamp each transaction, so it is possible to estimate average travel speeds for each individual trip. For other roads we have used GPS travel speed data from external provider TomTom to determine average travel speeds on Transurban assets.

Fuel type is also important in the calculation of GHG emissions. Vehicle fuel type is estimated from information on fleet mix and fuel type for each state and city documented in the 2016 Australian Bureau of Statistics (ABS) Motor Vehicle Census.

Transurban uses the above information and applies emission factors sourced from the University of South Australia that are sensitive to average travel speeds to calculate the GHG emissions from customer vehicles on the specified Australian roads.