Horizontal directional drilling (HDD) is a trenchless method used to install underground utilities like water pipes, sewer lines, and cables. This technique involves drilling a pilot hole along a predetermined path, which minimizes surface disruption and environmental impact. After the pilot hole is created, a larger reamer is pulled back through the hole to expand it. This allows for the installation of the utility line in a single continuous piece. HDD is commonly used in urban areas where traditional excavation would be impractical or damaging to existing infrastructure.