This study approaches terminology used in road traffic documents. It is demonstrated that this terminology shows variation which can be explained in different contexts related to the varied and evolving nature of technical language, new police practices, new traffic regulations and also to the important role played by international legislation. All these factors contribute to the emergence of new terms causing problems when looking for equivalents in several languages due to lack of harmonization. Based on this observation we have attempted to study the mechanisms of loans, neologisms and abbreviations. The definitions of the concepts are analysed in the Belgian legal framework of the Highway Code, the traffic laws and the implementing royal decrees. The analysis of the terminological enrichment process finally leads to an internal validation procedure described in the methodology that aims to ensure compatibility of the concept in the legal environment and stresses the importance of involving experts to clarify technical concepts for translators. Finally, it supports our initial hypothesis that it is possible to establish a reliability status depending on how deeply these terms are rooted in usage, police jargon and Belgian legislation.