The purpose of this Supplement is to provide supplementary guidance to [ITU-T L.1430] to help practitioners and organizations assess greenhouse gas (GHG) emission reduction potential enabled by an information and communication technology (ICT) based real-time navigation service (RNS).This Supplement illustrates general principles,concepts,requirements and methods for quantifying and monitoring GHG emission reductions or removal that result from an increased transportation efficiency due to the technological intervention of an RNS solution,one ICT application in the transport sector.[ITU-T L.1430] provides general guidance for assessing potential energy saving and GHG abatement achieved by ICT based projects.This Supplement intends to provide specific guidance for assessing energy savings and GHG abatement potential of an ICT project involving an RNS. Especially,this methodology focuses on an RNS based on the smart-phone appliance.Based on the experiences from a Korean study,this guidance describes how to indirectly estimate energy consumption reduction and GHG abatement potential related to RNS Future revisions may look into direct estimation methods.This Supplement intends to provide a general guidance for:?planning of a real-time navigation project and defining its baseline and project scenario;?quantifying GHG emission reduction enabled by the project activities;?managing data quality;?monitoring the project performance; and? validating quantification methods by applying the conservative principle.The intended audience of this Supplement is policy makers at the national level who might require information to design an effective climate change policy framework to utilize ICT enabled energy efficiency measures in the transport sector as well as practitioners and organizations developing and offering RNS.This Supplement might offer high relevancy to policy makers and technology advisors in intelligent transport system (ITS) domain.