Geometric Design

Vertical Curve are provided at the intersections of different grades to smoothen the vertical profile. The vertical curve used in the highway are of two types: Summit Curve, Valley Curve.

Design of Vertical Alignment Generally Highway is aligned to follow the natural topography keeping in view the drainage and other design consideration.   The vertical alignment of a highway affects: Acceleration & Deceleration Operational cost of vehicle Sight distance Vehicle speed The vertical alignment consist of two element: 1. Gradient 2. Vertical curve Gradient: It

Set Back Distance: It is clearance distance, required from the centre line of pavement/road to the obstruction in ode to maintain the adequate sight distance to the curve. The set back distance or clearance required from the centre line of horizontal curve depends upon. Required sight distance (SD) Radius of horizontal Curve (R) Length of

Transition Curves: When a vehicle traveling on a straight road enters into a horizontal curve instantaneously, it will ca discomfort to the driver. To avoid this, it is required to provide a transition curve. This may be provided either between a tangent and a circular curve or between two branches of a compound or reverse

ExtraWidening: Extra width provide to Road at horizontal curve is called extrawidening. It is provided for following purposes: To avoid off tracking due to rigidity of wheel base. To encounter psychological tendency of driver. To increase visibility at curve. To account lateral skidding. Off tracking: Path travelled by front axle and path travelled by rear

Method of Obtaining Superelevation: Introducing superelevation on a horizontal curve in the field is an important feature in construction. The full super-elevation is attained by the end of transition curve or at the beginning of the circular curve. The attainment of superelevation may be split up into two parts: Elimination of crown of the cambered

Design of  Superelevation⇒ Design of superelevation is a complex problem for mixed traffic conditions because different vehicles are moving with different speed hence the required superelevation are also different.        In this case IRC suggest to design the superelevation for 75% of the design speed considering coefficient of friction is 0. Step.1: The

Equilibrium Superelevation: Equilibrium superelevation is that superelevation at which pressure at the inner and outer tyre will be equal. if the coefficient of friction is neglected i.e. f =0 then, e=    , V in km/h This means that if a road surface is super elevated by tan-1  then the friction force will not be

Superelevation: The transverse inclination throughout the length of horizontal curve by raising outer edge counteract w.r.t. inner edge, in order to counteract the effect of centrifugal force is known as superelevation (or cant or banking). The superelevation ‘e’ is expressed as the ratio of height of outer edge w.r.t. the horizontal width, i.e Superelevation (e)=

Stability Analysis on Horizontal Curve without Superelevation: It is the curve in plane to provide change in the direction to Central line on the road. When a vehicle travel on a horizontal curve, the centrifugal force act horizontally outward through the center of gravity of the vehicle. The centrifugal force depends upon the speed of

Design of Horizontal Alignment: Various design element to be considered in the horizontal alignment are: Design speed Type and length of transition curve Width of pavement Super elevation Radius of circular curve Set back distance Design Speed: The design speed is main factor on which most of the geometric design element depends including horizontal elements.

Curve: Curves are provided in highways in order that the change of direction at the intersection of straight alignments either in horizontal or vertical plane, shall be gradual. The necessity of curves arises due to the following reasons: Topography of the country To provide access to a particular locality Restrictions imposed by property Preservation of

Intermediate sight distance (ISD): On a horizontal curve, the requirement of overtaking sight distance can not always be satisfied. In such cases overtaking is prohibited by using regulatory signs. To provide an opportunity for overtaking operation on horizontal curves or in restricted areas, we provide intermediate sight distance, i.e. equals to twice of stopping sight

Overtaking Sight Distance (OSD): If all the vehicle ply on the road at the design is speed, then theoretically there would be no need for overtaking, but practically it never happens, hence vehicle moving at design speed, has to overtaken the slow moving vehicle. The minimum distance open to the vision of the driver of

Stopping Sight Distance (SSD): The minimum distance visible to a driver ahead to safety stop a vehicle travelling at design speed without collision with any other obstruction is termed as “SSD”. It is also termed as “Absolute Minimum Sight Distance” or ” Non-Passing Sight Passing”. The stopping distance of vehicle include: Lag Distance () Braking

Sight Distance: Sight distance is the length of road visual a head to the driver at any distance. ( it is considered by taking the height of eyes of the driver to be 1.2 m and height of object to be 0.15 m). Restriction to the visibility/sight distance maybe caused in the following cases: At

Roadway / Width of Formation: It is the sum of with pavement or carriageway including separator (if any) and the shoulder. Roadways width is the top of highway embankment or bottom width of highway cutting excluding the side drain. Width of Formation of various class of Road are as follows: Right of Way / Road

Shoulder: Extra width provided adjacent to edge of pavement is called shoulder. It is provided for emergency point of view like Breakdown of vehicle, medical emergency etc.   As per IRC Minimum width of shoulder required for a highway is 2.5 meter. Cross slope of shoulder should be 0.5% more than cross slope of adjoining

Divider /Medians / Traffic separators Divider is an element provided to Road along the center line to separate two way traffic. The main function of median is to prevent “Head on collision” between vehicles moving in the opposite direction. it also serves following other functions: To channelize traffic into the streams. To protect the pedestrians.

Camber / Cross- Slope: It is the slope provide to the road surface in the transverse direction to drain the rainwater from the road surface to avoid the following: Stripping of bitumen from the aggregate in the presence of the water. In order to avoid swelling of sub grade in case water seeps up to