Drainage is one of the primary factors considered during the design of pavements. This paper presents the data from large-scale permeameter tests conducted on pavement sections to evaluate the drainage characteristic of geocomposite (GC) embedded subbase layers with and without traffic load. Two types of GCs with 2D core and 3D core were considered to enhance the drainage properties of a subbase layer. The large-scale permeameter test results indicate that the in-plane drainage capacity of the subbase layer improved by about 12 and 22 fold, respectively, for 2D−GC and 3D−GC. The GCs can drain infiltrated water at a rate of more than 300 m/day (in-plane permeability), even if the thickness of the subbase layer is reduced by about 50%. Over the pavement's design life, long-term in-plane permeability is estimated to decrease by 65–70%. It is estimated that the GC embedded subbase layers could drain off 50% of the infiltered water from a two-lane pavement system within 2 h, even after reducing the layer thickness by 100 mm. A set of new drainage coefficients for geocomposite improved subbase layers (m3c) were proposed based on the American Association of State Highway and Transportation Officials drainage quality guidelines. © 2022 Elsevier Ltd