With increasing market competition and environmental awareness, the freight transport industry has become under ever-increasing pressure to achieve better sustainability. Through horizontal transport collaboration (HTC), companies can consolidate their freight into fewer numbers of trucks, leading to cost and environmental savings. Therefore, HTC has been considered a promising strategy to boost the sustainability of freight transport. However, the successful applications of HTC are hampered by multiple barriers. This study contributes to the literature by identifying and prioritizing these barriers through integrating the fuzzy Delphi method (FDM) and the analytical hierarchy process (AHP). Firstly, a holistic list of 30 barriers divided into five categories is identified using literature review. Secondly, FDM is used to reach a consensus of experts' opinions regarding the important barriers that warrant undergoing the assessment process by AHP. Thirdly, AHP is used to identify the priority rankings of the five barrier categories and their associated barriers. Finally, the proposed approach is used to examine the critical HTC barriers in a case study from Denmark.