Question

Which of the following indicates correct Speed and Volume/Capacity Ratio respectively, for a road with Level of Service A?

• A. 120 km/hr and 0.8
• B. 80 km/hr and 0.6
• C. 60 km/hr and 0.85
• D. 70 km/hr and 0.70

Hint:

To easily remember Level of Service (LOS): - LOS A = Free Flow. The road is mostly empty, so the $V/C$ ratio is low ($\leq 0.6$) and drivers can travel at maximum safe speeds. - LOS F = Gridlock. The road is oversaturated, the $V/C$ ratio matches or exceeds 1.0, and speed drops toward zero.

Answer 1

The Correct Option is B

Concept: The Level of Service (LOS) framework, defined by the Highway Capacity Manual (HCM), is a qualitative measure used to describe operational conditions within a traffic stream. It rates driving conditions from LOS A (free-flowing traffic) to LOS F (forced or breakdown flow). The Volume-to-Capacity ratio ($V/C$) measures road congestion by comparing current traffic volume ($V$) against the maximum capacity ($C$) the road can handle: $$ \text{Ratio} = \frac{V}{C} $$

Step 1: Analyzing the characteristics of Level of Service A (LOS A).
LOS A represents ideal driving conditions, characterized by:
• Complete physical freedom to maneuver within the traffic stream.
• High travel speeds close to or at the design limit of the highway.
• Very low congestion levels, which means a low $V/C$ ratio (typically $\leq 0.60$).

Step 2: Evaluating the options based on $V/C$ thresholds.
Let us review the options using standard traffic performance criteria:
• Option (A) - 120 km/hr and 0.8: A $V/C$ ratio of 0.8 indicates that the road is reaching 80% of its capacity. This causes vehicles to bunch together, dropping the service level to LOS C or D.
• Option (B) - 80 km/hr and 0.6: A $V/C$ ratio of 0.6 indicates low congestion, allowing vehicles to maintain stable speeds (like 80 km/hr) with high maneuverability. This aligns with the requirements for LOS A.
• Options (C) & (D) - High $V/C$ ratios (0.85 and 0.70): These ratios represent higher traffic volumes relative to road capacity, which restricts driver freedom and corresponds to lower service levels (LOS B or C). Consequently, Option (B) provides the most accurate combination of speed and $V/C$ ratio for LOS A.