What are the different types of signal operations?

• A. Pretimed, demand, and semi-actuated
• B. Pretimed, fixed-time, and fully-actuated
• C. Pretimed, semi-actuated, and fully-actuated
• D. Pretimed, signalized, and un-signalized

Answer: (C)

The correct answer highlights the three primary types of signal operations that are commonly found in traffic management systems: pretimed, semi-actuated, and fully-actuated.

Pretimed signals operate on a fixed cycle length and provide green and red phases predetermined by traffic engineers based on expected traffic demand. This type of signal is advantageous in scenarios where traffic demand is consistent and predictable, allowing for simpler operations without the need for real-time adjustments.

Semi-actuated signals, on the other hand, are designed primarily for controlling major roadways while allowing for adjustments based on the presence of vehicles on the minor roadways. These signals utilize detection devices that sense vehicles waiting on the minor street and extend green time as needed to accommodate those vehicles.

Fully-actuated signals utilize vehicle detection for all approaches to the intersection. They adjust the signal phases in real-time based on actual traffic demand, optimizing flow for all vehicles and pedestrian movements. This system is particularly beneficial in dynamic traffic conditions where vehicle volumes can vary significantly throughout the day.

The other options presented include different combinations of terms that do not accurately represent the typical classification of signal operations. For instance, the reference to 'fixed-time' as a type of signal operation can be misleading, as 'pretimed' and 'fixed-time'