Inadequate and ineffective roadway and roadside drainage causes highway pavements to fail prematurely. For rehabilitation techniques to perform as desired, surface and subsurface drainage conditions must first be addressed. Mobile lidar is emerging as a safe and effective tool for collecting vast amounts of surface data that can assist in developing drainage designs. This paper presents a case study on the application of mobile lidar to develop a preliminary drainage design on US-75 in north Texas. A design is provided for an underdrain system that includes both longitudinal and lateral pipes. A roadside grading design is provided that works in concert with the underdrain design to move the water away from the pavement structure. Design constraints and challenges include a roadside ditch flow line higher than the pavement structure, slope stability concerns along the frontage road, front slope steepness along a high-speed corridor, and depth of cut within the pavement for installation of the underdrain. The preliminary design, developed from data collected with mobile lidar, was provided to the Texas Department of Transportation. This design has already been used to improve the drainage in the roadside ditch.