"Free-swinging" signal heads are typically located on which type of support system?

"Free-swinging" signal heads, also known as swinging signal heads, are typically located on span wire support systems. Span wires are utilized to suspend traffic signal heads above the roadway, allowing them to sway with the wind or during vehicular movement without being damaged. This design is particularly advantageous in locations with high winds or where poles cannot be easily installed.

The flexibility of the span wire system allows for easier installation and adjustment of signal heads. Additionally, it provides a stable support while still allowing for some movement. This setup is often used in urban environments where space is constrained, making span wires a practical solution.

On the other hand, while signal poles provide a fixed mounting option for signal heads, they do not allow for the "free-swinging" characteristic that span wires provide. Traffic cabinets and concrete bases serve different functions in traffic signal systems, not supporting the dynamic aspect of signal head positioning as span wires do.