Existing culverts are frequently retained and extended during highway widening endeavors. Numerous Reinforced Concrete Box Culverts (RCBCs) were initially constructed using a stepped approach, featuring a reduction in slab thickness as the embankment height decreases along the culvert. In widening projects, lightweight fill is commonly employed above the thinner culvert sections to avoid increasing the net load on the culverts. This web application has been designed to assist users in exploring diverse arrangements of lightweight materials situated within the current embankment boundaries, thereby facilitating the identification of viable lightweight fill configurations.