A bottleneck in traffic engineering occurs when which condition exists?

A bottleneck in traffic engineering occurs when which condition exists?

• A. Supply exceeds demand
• B. Demand exceeds capacity
• C. All vehicles travel at the same speed
• D. Traffic volume is zero

Answer: (B)

Bottlenecks appear when the amount of traffic trying to pass a point (demand) exceeds what the road segment can handle at that moment (capacity). Capacity is the maximum sustainable flow through the segment under current conditions; demand is how many vehicles want to use that segment. When demand is less than or equal to capacity, traffic can move through with little or no delay. But when demand surpasses capacity, a queue forms upstream, speeds drop, and delays accumulate—the telltale sign of a bottleneck. For example, a lane closure reduces capacity; if rush-hour demand remains high, the arrival rate overwhelms what the road can carry, creating a backlog. The other situations described—supply exceeding demand (underutilization), everyone moving at the same speed (not in itself causing a bottleneck), or zero traffic volume (no flow to constrain)—do not produce the congestion pattern characteristic of a bottleneck.

Bottlenecks appear when the amount of traffic trying to pass a point (demand) exceeds what the road segment can handle at that moment (capacity). Capacity is the maximum sustainable flow through the segment under current conditions; demand is how many vehicles want to use that segment. When demand is less than or equal to capacity, traffic can move through with little or no delay. But when demand surpasses capacity, a queue forms upstream, speeds drop, and delays accumulate—the telltale sign of a bottleneck. For example, a lane closure reduces capacity; if rush-hour demand remains high, the arrival rate overwhelms what the road can carry, creating a backlog. The other situations described—supply exceeding demand (underutilization), everyone moving at the same speed (not in itself causing a bottleneck), or zero traffic volume (no flow to constrain)—do not produce the congestion pattern characteristic of a bottleneck.