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Questions and Answers
What is the primary purpose of vertical curves in road design?
What is the primary purpose of vertical curves in road design?
- To improve road lighting
- To increase the road width
- To provide a smooth transition at grade changes (correct)
- To enhance road durability
Which type of vertical curve is generally considered aesthetically better?
Which type of vertical curve is generally considered aesthetically better?
- Curves with greater length (correct)
- Short curves
- Curves with sharp angles
- Steep curves
What does the term 'ruling gradient' refer to?
What does the term 'ruling gradient' refer to?
- A gradient which should never be exceeded in normal conditions (correct)
- The average gradient of a road
- A gradient used only in emergencies
- The steepest gradient that can be used in any part of the road
Under what conditions may limiting gradients be used?
Under what conditions may limiting gradients be used?
Which of the following describes exceptional gradients?
Which of the following describes exceptional gradients?
What is the minimum length for a vertical curve when the design speed is 40 km/h with a 1.2% maximum grade change?
What is the minimum length for a vertical curve when the design speed is 40 km/h with a 1.2% maximum grade change?
What does the term 'gradient' refer to in road design?
What does the term 'gradient' refer to in road design?
What should be considered when selecting the gradient for road design?
What should be considered when selecting the gradient for road design?
What is the maximum allowable length for exceptional gradients?
What is the maximum allowable length for exceptional gradients?
For design speeds up to 35 km/h and a maximum grade change of 1.5%, what is the minimum required length of the vertical curve?
For design speeds up to 35 km/h and a maximum grade change of 1.5%, what is the minimum required length of the vertical curve?
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Study Notes
Vertical Curves
- Vertical curves provide smooth transitions for grade changes on roads.
- Both summit and valley curves should be designed as parabolas for optimal functionality.
- Length is influenced by sight distance requirements; longer curves are not only more functional but aesthetically pleasing.
- Minimum lengths for vertical curves are specified for various design speeds and grade changes, ensuring safety and comfort.
Table 2.20: Minimum Length of Vertical Curve
- Design speeds up to 35 km/h with 1.5% maximum grade change require a minimum curve length of 15 meters.
- Design speeds of 40 km/h with a maximum grade change of 1.2% require at least 20 meters.
- For 50 km/h and a maximum grade change of 1.0%, a minimum length of 30 meters is necessary.
Gradient
- Gradient refers to the rate of rise or fall along a road, expressed as a ratio or percentage.
- Selection of gradient should consider design speed and terrain characteristics.
- Different types of gradients include:
- Ruling Gradient: Maximum gradient that should not be exceeded in normal conditions.
- Limiting Gradient: Steeper than the ruling gradient, allowable for restricted lengths due to terrain or cost constraints.
- Exceptional Gradient: Even steeper, permitted only in extraordinary situations and for short distances.
Guidelines for Use of Gradients
- Ruling gradients are standard; should be utilized for normal design procedures.
- Limiting gradients may be adopted where topography makes gentler gradients impractical, while minimizing the length of steeper sections.
- Exceptional gradients allowed for short stretches (max 100m) in difficult conditions.
- In mountainous terrain, segments of exceptional gradients must be separated by sections of gentler gradients, each at least 100 meters long.
Recommended Gradient Limits
- Maximum rise over a 2 km stretch should not exceed 100 meters in mountainous terrain, and 120 meters in steep terrain.
- In hilly areas, gradient design should minimize gear changes for heavy vehicles to enhance operational efficiency and reduce time.
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