Test: Highway Geometric Design -2 - Civil Engineering (CE) MCQ

Mechanical widening 
where, n = no. of lanes
For 10.5 m wide pavement,
n=3

Reaction time is an important factor when calculating the stopping distance of a vehicle. It represents the time it takes for a driver to perceive a hazard and respond accordingly.

The average reaction time is typically estimated at:

• 5 seconds: An unrealistic duration for most driving scenarios.
• 2.5 seconds: A more reasonable estimate for alert drivers.
• 0.5 seconds: This is exceptionally quick and unlikely for typical conditions.
• 10 seconds: This is far too long for practical driving.

For most driving situations, the reaction time of 2.5 seconds is often used in calculations.

Ruling gradient is the maximum gradient within, which the designer attempts to design the vertical profile of a road.

The Indian Roads Congress (IRC) recommends a maximum vehicle width of 2.44 meters (equivalent to 8 feet) to ensure compatibility with road infrastructure, lane designs, and safety standards. This width accommodates most commercial vehicles while preventing excessively wide vehicles from causing traffic hazards or structural issues.

• Option A (1.85 m): Too narrow for standard vehicles (even compact cars are typically wider).

• Option C (3.81 m) / D (4.72 m): Impractically wide for roads, exceeding typical lane widths.

• Option B (2.44 m): Matches IRC guidelines and aligns with international standards for vehicle width limits.

The correct answer is B, as it reflects the IRC’s prescribed maximum vehicle width for safe and efficient road use.

Transition curves are introduced between straight road sections and circular horizontal curves to gradually change the curvature, ensuring a smooth transition for vehicles. This design:

• Reduces jerk (rate of change of acceleration) by avoiding abrupt shifts in lateral forces.

• Enhances safety and comfort by preventing sudden steering adjustments or passenger discomfort.

Why Other Options Are Incorrect:

• A: Transition curves aim to lower jerk, not increase it.

• B: They lengthen the overall curve, not minimize it.

• C: While they aid in alignment, their primary purpose is dynamic (safety/comfort), not construction simplicity.

The correct answer is D, as transition curves mitigate abrupt changes in acceleration, aligning with engineering standards for safe road design.

Transition curves are introduced in horizontal alignment to gradually transition the road from a straight section to a curved section. Their primary purposes include:

1. Enabling smooth application of superelevation: Superelevation (road banking) cannot be applied abruptly. Transition curves allow a gradual increase or decrease in cross-slope, ensuring vehicles adapt safely to the curve.

2. Providing a gradual change in curvature: This avoids sudden lateral forces, improving comfort and safety.

Why Other Options Are Incorrect:

• A: Transition curves do not increase the radius of curvature; they connect a straight path (infinite radius) to a fixed-radius circular curve.

• C: Centrifugal force is counteracted by superelevation and friction, not directly by the transition curve.

• D: Skid prevention is achieved through proper superelevation and friction, but transition curves themselves ensure these elements are applied smoothly.

The correct answer is B, as transition curves are essential for the controlled and gradual implementation of superelevation, aligning with safe and efficient road design principles.

Vertical curve:

Vertical alignment is the elevation of the centerline of the road. It may be in the form of a circular arc or a parabola

The vertical curve is divided into two categories

1) Summit curve:

It is a crest curve with convexity upward.

The deviation angle between the two interacting gradients is equal o the algebraic difference between them.

When an ascending gradient meets with descending gradients the deviation angle will be maximum

N = n1 – (-n2) = n1 + n2

Ideal shape of summit curve is circular. 

But Square parabola is the best shape of the summit curve due to good riding qualities, simplicity of calculation, and uniform rate of change of grade.

2) Valley curve:

The maximum possible deviation angle is obtained when a descending gradient meets with an ascending gradient.

The overtaking sight distance is not included in the valley curve.

The cubic parabola is generally preferred.

The headlight sight distance available at the valley curve should be at least equal to the stopping sight distance.

When a fast moving vehicle travels along a summit curve, the centrifugal force will act upwards, against gravity and hence a part of the pressure on the tyres and spring of the vehicle suspensions in relieved. So there is no problem of discomfort to passengers on summit curves, particularly because the deviation angles on roads are quite small. The only problem is designing summit curves is to provide adequate sight distances. The stopping sight distance or the absolute minimum sight distance should invariably be provided at all sections of the road system and so aiso on summit curves.