The basis for the ISO standard was already laid in 2014: an industry working group was commissioned by the European Commission to consider the principles. 

The key question was “if multiple shipments are transported in a vehicle in a round trip for multiple customers (milk run/distribution), how do you distribute the CO2 emissions of that entire trip over the shipments?”.  The question is not how much CO2 the vehicle emitted in that journey: it is easy to answer. The question from the customers is more difficult “how much CO2 emissions did it cost to bring my shipment from origin to destination?”. 

The COFRET working group has found a simple answer: they have looked at the way to calculate cost prices. The further away a shipment is taken, and the more capacity of the vehicle is used for that shipment, the higher the cost. This can be translated into “the further away the shipment is taken, and the more capacity of the vehicle is used, the greater the allocated part of the emissions of the trip”.   

Why capacity and not weight (tons?): sometimes you can no longer add a load because the vehicle is full, not because the maximum loading weight has been reached. A very large box with little weight is therefore allocated more CO2 than a small heavy box: that makes sense. This guideline contains more information on how this works. 

The transport chain consists of several steps, including storage and transhipment. If each step measures the emissions per shipment, you can add the steps to the emissions across the entire chain, for that specific shipment. That sounds simple: putting it into practice make you run into all kinds of implementation questions. Fortunately, a lot of experience has been gained in recent years on how to solve these practical questions. 

The application guidelines can be found on www.carbonfootprinting.org/en/guidelines/. With the help of these guidelines software can be made that can implements the ISO standard.