Which term describes the observed reduction in capacity when traffic is congested?

Which term describes the observed reduction in capacity when traffic is congested?

• A. Capacity gain
• B. Throughput increase
• C. Capacity drop
• D. Free-flow rate

Answer: (C)

In traffic engineering, the observed decrease in how much traffic can pass a point when conditions become congested is called capacity drop. Capacity describes the maximum sustained flow (vehicles per hour) a section of road can support. When a jam forms or congestion spreads, speeds fall and vehicle interactions increase, so fewer vehicles can pass per hour than in free-flow conditions. That reduction from the free-flow capacity to the lower congested capacity is the capacity drop. So the term that best fits this phenomenon is capacity drop. The other terms don’t fit: capacity gain would imply more capacity under congestion, which isn’t observed; throughput increase would mean more vehicles passing, which contradicts the idea of congestion reducing flow; and free-flow rate is the higher rate present when there is no congestion, not the reduced rate during congestion.

In traffic engineering, the observed decrease in how much traffic can pass a point when conditions become congested is called capacity drop. Capacity describes the maximum sustained flow (vehicles per hour) a section of road can support. When a jam forms or congestion spreads, speeds fall and vehicle interactions increase, so fewer vehicles can pass per hour than in free-flow conditions. That reduction from the free-flow capacity to the lower congested capacity is the capacity drop.

So the term that best fits this phenomenon is capacity drop. The other terms don’t fit: capacity gain would imply more capacity under congestion, which isn’t observed; throughput increase would mean more vehicles passing, which contradicts the idea of congestion reducing flow; and free-flow rate is the higher rate present when there is no congestion, not the reduced rate during congestion.