This document provides an overview of geometric design considerations for highways, including cross-sectional elements, sight distances, and horizontal and vertical alignments. It discusses design of horizontal curves, which can be circular, compound, or reverse/serpentine, as well as transition curves. Vertical alignment depends on gradients and curves, with descriptions of average, ruling, limiting, exceptional, floating, and minimum gradients. Grade compensation is explained to reduce combined resistance from ruling gradients and curved alignments. Finally, it covers vertical curves, distinguishing between summit/crest curves and valley/sag curves.

1. Welcome to Civil Genics...

2. Geometric Design of Highways
(contd.)
Concerned with; Cross sectional elements
Sight distance
Horizontal & Vertical alignment

3. Horizontal and vertical alignments
Curves horizontal
vertical
• Extra widening of curves
Mechanical reasons (wm) ‘off tracking’
psychological reasons (wps)

4. Horizontal Curves
Circular simple, compound & reverse/serpentine curve
Transition
• Simple curve – single radius
• Compound curve – multiple radius
• Reverse / serpentine curve – single or various radius comes under combination of
arcs
Transition curve
Between straight & a circular curve or two
branches of reverse or compound curves.
Types; spiral
Lemniscates
Cubic parabola = L2/24R

6. Vertical Alignment
Elevation or side view of centre line of road. It depends gradients and curves.
Gradients
• rate of rise or fall with respect to horizontal alignment of road.
• Representation - 1V to 'n' H
types; average gradient - (total rise or fall / total length)
ruling gradient - (maximum/permissible gradient - to be designed)
limiting gradient - (steeper than ruling gradient)
exceptional gradient - (should not be > 100m)
floating gradient - (combination of rise & fall - less effort)
minimum gradient - (to avoid drainage problems)

7. • Grade compensation – combined
resistance due to ruling gradient and
curved alignment exceeds the pulling
over of vehicles. There the ruling
gradient is reduced to keep combined
resistance in permissible limit.
formula = (30+R)/R; to
maximum value of 75/R
for ruling gradient < 4% - grade
compensation is not required
Vertical curves
Summit curves or crest curves
Valley curves or sag curves
• Ascending gradient meet descending
gradient or two descending gradients
follows – summit curves
• Descending gradient meet ascending
gradient or two ascending gradients
follows – valley curves

8. Thank you..