Vertical Alignment PDF

VERTICAL ALIGNMENT TERRAIN Level Terrain - is that condition of the highway sight distances on generally long or could be made to be so without major expense. TERRAIN Rolling Terrain – is that condition when the natural slope consistently rise above or fall below the road grade TERRAIN...

VERTICAL ALIGNMENT TERRAIN Level Terrain - is that condition of the highway sight distances on generally long or could be made to be so without major expense. TERRAIN Rolling Terrain – is that condition when the natural slope consistently rise above or fall below the road grade TERRAIN Mountainous Terrain – is that condition when longitudinal and transverse changes in the elevation of the grand with respect to the road. DESIGN ELEMENT Vertical alignment of highways consists of gradients grade compensation vertical curves (valley curve, summit curve). RULING GRADIENT It is also called as designer gradient. the maximum gradient which is generally used to design the vertical profile of highway RULING GRADIENT the maximum gradient which is generally used to design the vertical profile of highway. It depends on the terrain, length of the grade, speed, pulling power of the vehicle and the presence of the horizontal curve. LIMITING GRADIENT Provided as shorter stretches in highways. This gradient is adopted frequently in terrains with limited stretches. EXCEPTIONAL GRADIENT These are very steeper gradients given at unavoidable situations and they are adopted for stretches not exceeding 100m of length. MINIMUM GRADIENT Used in draining of rainwater from the road. For lateral drainage, Camber is provided. But for the longitudinal drainage along the side drains require some slope for smooth flow of water. For concrete drains minimum gradient of 1 in 500 and open soil drains gradient of 1 in 200 is suitable. AVERAGE GRADIENT It is the ratio of total rise or fall to the horizontal distance between any two points along the alignment of the road. VERTICAL CURVES Generally, two types of vertical curves are there to adopt for the vertical alignment. They are summit curve and valley or sag curve. VERTICAL CURVES Generally, two types of vertical curves are there to adopt for the vertical alignment. They are summit curve and valley or sag curve. SUMMIT or CREST CURVE A vertical curve adopted mainly when the gradient is upwards. In case of summit curve simple parabola is considered as best curve shape. It connects inclined sections of roadway, forming a crest, and they are relatively easy to design. VALLEY OR SAG CURVE It is a vertical curve provided when the gradient is downwards. Generally, when the vehicle meets downward gradient it accelerates more, and discomfort arises. So, in the design of valley curve in vertical alignment comfort is considered along with sight distance. SIGHT DISTANCE FOR VERTICAL CURVES  A 5% grade intersects a -3.4% grade at station 1+990 of elevation 42. 3 m. Design Velocity = 60 kph Height of driver’s eye from road pavement = 1.37 m Height of an object over the pavement ahead = 100 mm Perception – reaction time = ¾ s Coefficient of friction between the road pavement and tires = 0.15 Determine the stopping sight distance and required length of curve. GENERAL CONTROLS A smooth grade line with gradual changes should be sought for in prefe rence to a line with numerous breaks /short length of grades. The ‘roller coa ster” or the hidden – dip type of profile should be avoided. GENERAL CONTROLS Undulating grade line involving substantial length of momentum grades should be evaluated for their effect on traffic operation. (Bumpy area) GENERAL CONTROLS A “broken – back” grade line should be avoided. On long grades, it may preferable to place the steepest grades at the bo ttom and flatter the grades near the top of the ascent. Where at-grade intersections occur on roadway sectors with moderate to steep grades, it is desirable to reduce the grades through the intersection. Sag vertical curves should be avoided in cuts unless adequate drainage can be provided. COORDINATION OF HORIZONTAL AND VERTICAL ALIGNMENTS 1. Don’t put sharp horizontal curve at crest or sag 2. Don’t put the inflection point of a reverse curve at the crest or sag 3. Don’t repeat the crest and sag in same horizontal curve 4. Don’t put the sag in the long stretch of straight section (road would look bent) 5. Don’t put short straight section in broken-back curve