The European Norm EN 16258 was published in 2012 to provide a common methodology for the calculation and declaration of energy consumption and greenhouse gas emissions related to any transport operation. The objective was to offer a pragmatic and scientifically-acceptable approach that allows a wide group of users to prepare standardized, accurate, credible, comparable, and verifiable energy consumption and emission declarations. However, in its current form, EN 16258 contains gaps and ambiguities, and leaves room for interpretation, which makes comparisons of supply chains difficult. This research aims to overcome the shortcomings in the domain of allocating emissions from road freight transport operations to single shipments. Based on a discussion of emission drivers and the results of numerical experiments comparing the allocation vectors created by the EN 16258 allocation rules with those generated by the Shapley value, which is claimed to be the benchmark, 'distance' is identified as the single most useful unit for bridging the trade-off between accuracy and simplicity better than the other recommended allocation schemes. Thus, this paper claims that future versions of EN 16258 should only allow the allocation unit 'distance.' This will promote the accurateness, simplicity, consistency, transparency, and comparability of emission declarations. (C) 2016 Elsevier Ltd. All rights reserved.