What does Free Flow Speed (FFS) refer to?

Free Flow Speed (FFS) is defined as the theoretical speed of traffic flow under ideal conditions where there are no restrictions or obstructions, allowing vehicles to travel at their desired speeds. This concept is significant in traffic engineering and transportation planning, as it helps in determining the capacity and performance measures of roadways.

When conditions are optimal, such as when there are minimal vehicles on the road, no stoplights, and no other inhibiting factors, FFS reflects how fast vehicles can travel. Understanding FFS is essential for designing roadways, optimizing traffic operations, and implementing effective traffic management strategies.

The other options do not capture this specific definition effectively. For instance, while heavy traffic can indeed lead to slower average speeds, that scenario would not reflect the free flow condition. The speed limit on expressways is a regulatory measure rather than a reflection of ideal traffic conditions. Lastly, responding to emergencies is tied to practical limitations that would not define the theoretical nature of FFS. Thus, the choice that accurately encapsulates the concept is the theoretical speed of traffic flow under ideal conditions.