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Questions and Answers
What is the perceived reaction time to determine stopping sight distance?
Which type of grade profile should be avoided due to safety concerns?
For the design of vertical curves, which condition is emphasized for traffic operation?
In terms of vertical alignment, which curve placement is advisable?
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Which of the following is a recommended practice for horizontal and vertical alignment coordination?
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What condition is described as having consistently rising or falling slopes relative to the road grade?
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What is the primary purpose of the minimum gradient in road design?
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Which type of vertical curve is adopted primarily when the gradient is upwards?
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Which gradient is typically utilized for short stretches of highway where a steep slope is unavoidable?
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What is the ruling gradient primarily dependent on?
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What is the suitable minimum gradient for open soil drains?
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In vertical alignment design, what differentiates the valley curve from the summit curve?
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What defines the average gradient in road design?
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Study Notes
Terrain
- Level Terrain: Sight distances are long and can be achieved without significant expense.
- Rolling Terrain: Consistent rises and falls in elevation relative to the road grade.
- Mountainous Terrain: Significant changes in elevation, both longitudinally and transversely, relative to the road.
Design Elements
- Vertical Alignment: Includes gradients, grade compensation, and vertical curves.
Ruling Gradient
- Also known as the designer gradient.
- The maximum gradient used for designing the vertical profile of a highway.
- Depends on factors like terrain, grade length, speed, vehicle pulling power, and presence of horizontal curves.
Limiting Gradient
- Used for shorter stretches of highways.
- Implemented in areas with limited terrain stretches.
Exceptional Gradient
- Used for unavoidable situations with steeper gradients.
- Adopted for stretches no longer than 100 meters.
Minimum Gradient
- Ensures rainwater drainage from the road.
- Required for longitudinal drainage, utilizes side drains with a specific slope.
- Concrete drains need a minimum gradient of 1:500, while open soil drains need 1:200.
Average Gradient
- The ratio of total rise or fall to the horizontal distance between two points on the road alignment.
Vertical Curves
- Two main types: Summit (crest) curve and Valley (sag) curve.
Summit Curve
- Used when a gradient is upwards.
- Utilizes a simple parabola for its curve shape.
- Connects inclined sections forming a crest and is relatively easy to design.
Valley or Sag Curve
- Used when a gradient is downwards.
- Designed to provide comfort for drivers as deceleration occurs on a downward gradient.
Sight Distance for Vertical Curves
- A 5% grade intersects a -3.4% grade at station 1+990 with an elevation of 42.3 meters.
- Design velocity is 60 kph.
- Driver's eye height is 1.37 meters from the pavement.
- Object height over the pavement is 100 millimeters.
- Perception-reaction time is ¾ seconds.
- The coefficient of friction between pavement and tires is 0.15.
General Controls
- Seek gradual changes in grade lines, avoiding sharp breaks.
- Avoid roller coaster-like profiles with hidden dips.
- Minimize undulating grade lines with substantial momentum grades as they affect traffic operation.
- Avoid broken-back grade lines.
- Place steeper grades at the bottom of a long grade and flatter grades near the top.
- Reduce grades through at-grade intersections on moderate to steep slopes.
- Avoid sag vertical curves in cuts unless adequate drainage is provided.
Coordination of Horizontal and Vertical Alignments
- Avoid sharp horizontal curves at the crest or sag of a vertical curve.
- Avoid placing the inflection point of a reverse curve at the crest or sag.
- Prevent repeating crest and sag features on the same horizontal curve.
- Don't position sags in long stretches of straight sections.
- Avoid short straight sections within broken-back curves.
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Description
Explore the key concepts of highway design, including various terrain types and alignment techniques. This quiz covers the principles of ruling, limiting, exceptional, and minimum gradients as they relate to effective roadway design. Test your understanding of how these factors influence highway engineering.
