Presentation Title

Guidelines for Design Of Horizontal Curves For Highways And Design Tables IRC : 38-1988Presented To Gaurav Vaidya Assistant Professor, Planning1School Of Planning And Architecture, Bhopal February 2, 2015

Presented By Vishal Chettry 2014murp001Shubhankar Kumar 2014murp002ContentsOverviewHorizontal Curves And Its NeedGeneral Principles To Be FollowedSuperelevationMethod Of Building SuperelevationWidening Pavements On CurvesSet-Back Distance At Horizontal CurveSchool Of Planning And Architecture, Bhopal2Source - IRC : 38-1988 2OverviewOne of the most important element in designing the highway.Essential for smooth and safe driving especially when the traffic is moving at high speeds.Readymade tables for standardization for horizontal curves were brought out by the Indian Road Congress in 1970 as IRC : 38-1970 Design tables for Horizontal Curves For Highways.Previously it was in FPS units later it was converted to metric systems.The aim is to provide gentle slopes and mild curves that fit the natural terrain and are more aesthetic.School Of Planning And Architecture, Bhopal3Source - IRC : 38-1988 3Horizontal Curves And Its NeedHorizontal curves are abstract composition is space, which is not necessary to be seen but is felt by the driver while tilting, turning, dropping and climbing while travelling in the roads.Due to change in direction because of the topography, environmental, monuments etc.Allowing a vehicle to negotiate a turn at a gradual rate rather than a sharp cut.

School Of Planning And Architecture, Bhopal4

Source - IRC : 38-1988 4General principles to be followedSharp horizontal curves should be avoided at or near the apex of marked summit vertical curves for safety considerations.When vertical curves superimposes over the Horizontal curves gives a pleasing effect.The vertical and horizontal curves should coincide as far as possible and their length should be more or less equal.The degree of curvature should be in proper balance with the gradients.Straight alignments or flat horizontal curves at the expense of steep or long grades in a road with flat grades should be avoided. School Of Planning And Architecture, Bhopal5Source - IRC : 38-1988 5SuperelevationThe inward tilt of the road surface to attain equilibrium while turning a vehicle around a curve is called as superelevation.It is also required to prevent skidding on the roads.School Of Planning And Architecture, Bhopal6

Source - IRC : 38-1988 6Method Of Building SuperelevationSchool Of Planning And Architecture, Bhopal7

Source - IRC : 38-1988 7Widening Pavements On CurvesSchool Of Planning And Architecture, Bhopal8NECESSITY Movement of vehicle around the curves, rear wheels tracks inside the front wheels when curve is not superelevated but on the superelevated curves the relative position of the wheels depends on the speed and the friction developed. Greater the speed of the vehicle more it tends to move out. Hence widening is required.Difficulty in steering the vehicles to keep to the central line of the road.Requirement of greater clearances than on the straight roads.

Source - IRC : 38-1988 8Widening Pavements On CurvesSchool Of Planning And Architecture, Bhopal9

Source - IRC : 38-1988 9Set-Back Distance At Horizontal CurveSchool Of Planning And Architecture, Bhopal10Distance from the road Centre line within which the obstructions should be cleared to ensure the needed visibility i.e. the set-back distance.

Source - IRC : 38-1988 10Transition Curves School Of Planning And Architecture, Bhopal11

Transition curve is provided to change the horizontal alignment from straight to circular curve.11Method Of minimizing the Shock School Of Planning And Architecture, Bhopal12Reduction of Speed of vehicle. Taking a new path with greater radius of curve. Combination of (1) and (2). Designing the alignment with a radius of curvature gradually changing from infinity to the designed radius. 12Advantages of Transition curves School Of Planning And Architecture, Bhopal13Enabling the driver to turn steering wheel gradually, the transition permits the gradual application of super elevation necessary for self driving. Improve the aesthetics of road. When the circular curve joins a straight path, an optical illusion of a bulge is generally produced. If transition introduced this deceptive appearance will be eliminated. 13Requirement for Transition curves School Of Planning And Architecture, Bhopal14Radius of curvature should decrease gradually from infinity to the minimum to enable steering wheel to be turned gradually and to eliminate the shock due to application of centrifugal force. Radius of curvature should be inversely proportional to the length of the curve from the starting point. 14Considerations for Transition curves School Of Planning And Architecture, Bhopal15Rate of change of centrifugal acceleration. Rate of change of super elevation. Minimum Length of transition. Case Where No Transition Is Required. On National Highway, for a curve of 1200M, the design speed for which is 80 kmph, the centrifugal ratio that will develop equal to 0.042. 15Transition For Hair Pin Bends. School Of Planning And Architecture, Bhopal16A hairpin bend may designed as a circular curve with transition curve at each ends. Design considerations Minimum design speed - 20 kmph Minimum radius of inner curve - 14 m Minimum length of transition - 15 m Gradient Minimum 0.5 % Maximum 2.5 % Super elevation 10% Minimum Roadway width N.H / S.H 11.5m for double lane 9m for single lane Major District Road 7.5 m Village Road 6.5 m

16School Of Planning And Architecture, Bhopal17Thank you.17