Question

What is the primary factor affecting the capacity of urban roads during peak hours?

• A. Vehicle type
• B. Traffic signals
• C. Pavement condition
• D. Pedestrian crossings

Hint:

In urban areas, intersections are often the primary bottlenecks, and traffic signals at these intersections regulate flow. During peak hours, the ability of these signals to manage high traffic volumes efficiently directly determines the road's capacity. Factors like signal timing, cycle length, and coordination are paramount.

Answer 1

The Correct Option is B

Step 1: Understand Road Capacity and Peak Hour Conditions.
Road capacity refers to the maximum number of vehicles or persons that can be accommodated by a given section of a road or traffic lane in a given time period under prevailing road and traffic conditions. During peak hours, traffic demand is high, and the road network's ability to handle this demand becomes critical.
Step 2: Analyze how each factor affects urban road capacity during peak hours.

• (1) Vehicle type: While the mix of vehicle types (e.g., cars, trucks, motorcycles) affects the "passenger car equivalent" and thus the effective capacity, it is generally a secondary factor. Urban roads are designed for a mixed traffic flow, and the impact of vehicle type is usually accounted for in design. Its effect is often less dominant than other factors in determining primary bottlenecks during peak hours.
• (2) Traffic signals: Traffic signals are a primary control mechanism on urban roads. During peak hours, the green time allocation, cycle length, and coordination of traffic signals directly dictate how much traffic can pass through intersections. Signals introduce inevitable delays and queues. Poor signal timing or lack of coordination can severely limit the capacity of an entire road network, even if the physical road segments have ample width. Therefore, traffic signals are a critical bottleneck and a primary factor affecting capacity during peak hours.
• (3) Pavement condition: Pavement condition (e.g., presence of potholes, roughness) can affect vehicle speeds and ride quality. Extremely poor pavement can reduce capacity by slowing down traffic, but in most urban areas, pavements are maintained to a reasonable standard. Its impact on capacity, especially during peak hours when flow is already restricted by intersections, is generally less significant than that of traffic signals.
• (4) Pedestrian crossings: Pedestrian crossings, especially uncontrolled ones or those with frequent pedestrian activity, can interrupt traffic flow and reduce capacity. However, in comparison to the pervasive and often rigid control exerted by traffic signals on an entire urban network, pedestrian crossings (unless extremely frequent and poorly managed) typically have a localized impact. Signalized intersections manage both vehicular and pedestrian movements, making the signals themselves the primary control.

Step 3: Conclude the primary factor.
During peak hours, urban roads are typically constrained by their intersections, which are often controlled by traffic signals. The efficiency of traffic signal operation (timing, coordination) directly controls the flow of vehicles and is the most significant factor determining the effective capacity of urban roads. $$\boxed{\text{Traffic signals}}$$