Traffic signals are often controlled by devices that detect traffic and are placed:

Traffic signals are controlled by a variety of detection devices that help manage the flow of vehicles and pedestrians. These devices can be strategically placed under the pavement, which allows them to sense the presence of vehicles waiting at an intersection. Inductive loops, for instance, are commonly installed beneath the asphalt and use a change in magnetic field to detect a car's presence.

In addition, detection devices can also be placed overhead, such as in the form of video cameras or infrared sensors. These overhead devices can provide real-time monitoring of traffic conditions and adjust signal timing accordingly to improve traffic safety and efficiency.

Therefore, both the placement of devices under the pavement and over the roadway contribute effectively to the control and management of traffic signals, making the combined option comprehensive.