Intrusion of water through longitudinal joints can cause premature distress in hot mix asphalt (HMA) pavements. Similar to mat permeability, joint permeability is a critical factor governing the performance of HMA pavements. Hence, joint permeability should be used as a measure of quality of joint construction. In this ongoing study, a simple and effective permeameter has been developed, and used in a rational method to evaluate the permeability of longitudinal joints, relative to the permeability of the adjacent mat. The permeameter consists of three standpipes, which can be used for measuring the flow of water through a joint and through the mat on either side of the joint. Results from testing on several projects show that this permeameter can be used successfully to determine permeability of joints. The testing performed in this study shows that joints have significantly higher permeability compared to adjacent mats, different types of joints have different permeabilities and that treatment of joints with sealers and using improved joint construction techniques such as joint heater can reduce the permeability significantly. More testing of joints is being carried out, with the objective of developing specific criteria for using the joint permeameter for quality control of construction of longitudinal joints.