Every option combination, its own CO₂ figure

Under WLTP a manufacturer proves the CO₂ and fuel consumption of a family of vehicles by testing two extremes, a high and a low, and interpolating for every combination of options between them. A model-year change can touch thousands of combinations, because every option, whether it is wheels, aerodynamic parts or mass, moves the road load of the vehicle.

The manufacturer kept the interpolation in a workbook that grew by a sheet every year. The technical service that approves the figures had to be walked through it, and a change to one option meant regenerating files by hand, in the order that the workbook happened to require.

GraphAtlas WLTP takes the test results and the option lists as data, works the road load and the interpolation line for each vehicle in the family, and returns a figure for every combination with a reference to the test and the line that it came from. The method is the procedure of the regulation, followed step by step, and a step that the regulation leaves to judgement is shown as a choice, with the choice recorded.

The technical service reviews the procedure once, as code and text side by side, and checks a sample of combinations against it. Everything after that is a comparison of receipts.

The files for the last model-year change were assembled in two days, where the year before they had taken three weeks. The type-approval update carried 9,412 individual figures, and the technical service could trace every one of them to a test.

Homologation has since moved the same method into the configurator that sales uses, so that the figure a customer sees for the car they have specified is the figure that was approved for it.