Which of the following equipment is NOT typically seen at the construction site of a traffic signal?

The choice of grader as equipment not typically seen at a traffic signal construction site is valid because graders are primarily used for preparing and maintaining road surfaces by leveling and grading the existing ground. Their role is more common in broader road construction and maintenance projects rather than specific traffic signal installations.

In contrast, horizontal boring machines are essential for laying conduits under the pavement without disturbing the surface, making them crucial for traffic signal installations. Aerial lift trucks provide necessary access for tasks such as installing and maintaining signal heads and overhead signage, which are common in the traffic signal setup process. Additionally, trenchers are specifically designed to create narrow trenches to lay cables, making them indispensable for installing the electrical components of traffic signals. Thus, while the other options are integral to the installation process, the grader's function does not align with the specific needs of traffic signal construction.