TIM & DEFRA: Distance Changes

Summary of Changes

We have updated the distance calculation methodology in the Travel Impact Model (TIM) API to enhance accuracy and better align with external recommendations. These changes impact the way Great Circle Distance (GCD) is provided and how DEFRA uplift factors are applied:

1. Removal of ICAO Correction in API Responses

Previously, the TIM API applied corrections based on ICAO guidelines to the Great Circle Distance (GCD) provided in the API response. As part of this update:

• We now exclusively provide the raw GCD for flights.

• Corrections or adjustments for specific use cases, such as flight path deviations, are no longer included in the default API output.

This change simplifies the model and ensures transparency by returning the raw GCD, allowing users to apply their own adjustments as needed.

2. DEFRA Uplift Factor Application

For flights requiring DEFRA-compliant emissions reporting:

• Previously, the GCD distance was directly used for DEFRA distance reporting.

• Now, an 8% uplift factor is applied to the GCD, in line with DEFRA's recommendation to account for indirect routing and operational inefficiencies.

This adjustment aligns the TIM outputs with DEFRA’s updated guidelines and enhances the accuracy of emissions reporting for users requiring DEFRA-compliant data.

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Implications for Users

• Developers using the TIM API should note that raw GCD is now provided by default. Any additional corrections must be implemented client-side, depending on specific requirements.

• Users reporting emissions under DEFRA will automatically benefit from the 8% uplift factor applied to GCD for more accurate and compliant reporting.

For further details, please refer to the updated TIM API documentation and Greenhouse gas reporting: conversion factors 2024 by DEFRA.