Geometric Design of highway (Design controls and criteria) Introduction , elements, design speed, topography,traffic factors

1. DEPARTMENT OF
CIVIL ENGINEERING
Geometric Design of Highways
(Design Controls and Criteria)
Er. Ramprasad Kumawat
M.Tech

2. Geometric Design of Highways
• The highway crosses sectional elements
• - Camber
• -Sight Distance
• - Types of sight distances
• –Design of horizontal alignments
• - Super elevation,
• Widening of Pavements on horizontal curves
• - transition Curves
• - Design of Vertical alignments
• – Gradients
• - summit and Valley Curves
• - Recommendations of IRC Codes of Practice.

3. INTRODUCTION
• Importance of Geometric Design
• Geometric design of a highways deals with the
dimensions and layout of visible features of
the highway such as horizontal and vertical
alignments, sight distances and intersections.

4. • The geometries of highway should be designed
to provide efficiency in traffic operations with
maximum safety at reasonable cost.
• The designer may be exposed to either
planning of new highway net work or
improvement of existing highways to meet the
requirements of the existing and the
anticipated traffic

5. Geometric design of highways deals
with following elements
• (i) Cross section elements
• (ii) Sight distance considerations
• (iii) Horizontal alignment details
• (iv) Vertical alignment details
• (v) Intersection elements

6. • Under cross section elements, the
considerations for the width of pavement,
formation and land, the surface characteristics
and cross slope of pavement are included.
• The sight distance or clear distance visible
ahead of a driver at horizontal and vertical
curves and at intersections govern the safe
movements of vehicles.

7. Design Controls and Criteria
• The geometric design of highways depends on
several design factors.
• The important factors which control the
geometric elements are:
• (a) Design speed
• (b) Topography or terrain
• (c) Traffic factors
• (d) Design hourly volume and capacity
• (e) Environmental and other factors

8. Design speed
• The design speed is the most important factor
controlling the geometric design elements of
highways.
• The design speed is decided taking into
account the overall requirements of the
highway.
• In India, different speed standards have been
assigned depending upon the importance or the
class of the road such as National/State
Highways, Major/Other District Roads and
Village Roads.

9. • Further the design speed standards are
modified depending upon the terrain or
topography.
• Similarly urban roads have a different set of
design speeds.

10. Topography
• The topography or the terrain conditions
influence the geometric design of highway
significantly.
• The terrains are classified based on the general
slope of the country across the alignment, as
plain, rolling, mountainous and steep terrains.
• The design standards specified for different
classes of roads are different depending on the
terrain classification.

11. • For example the design or ruling speed of NH and
SH on plain terrain with general cross slope up to
10% is 100 kmph whereas
• The speed on rolling terrain with general cross
slope of 10 to 25% is 80 kmph and
• That on mountainous terrain with cross slope 25
to 60% is 50 kmph.
• As the speed standards affect geometric design
element, topography also affects the geometric
design of loads.
• Further in hilly terrain, it is necessary to allow for
steeper gradients and sharper horizontal curves
due to the construction Problems.

12. Traffic factors
• The factors associated with traffic that affect
geometric design of roads are the vehicular
characteristics and human characteristics of
road users.
• It is difficult to decide the design vehicle or
the standard traffic lane under the 'mixed
traffic flow condition prevalent especially on
urban roads of developing countries like India.
• This is a complex problem.

13. • The different vehicle classes such as passenger
cars, buses, trucks, motor cycles, and various
other types of non-motorised vehicles have
different speed and acceleration
characteristics, apart from having different
dimensions and weights

14. Design hourly volume and capacity
• The traffic flow or volume keeps fluctuating with
time, from a low value during certain off-peak
hours to the higher flow during the peak hours.
• It will be uneconomical to design the roadway
facilities for the peak traffic flow or the highest
hourly traffic volume.
• Therefore a reasonable value of traffic volume is
decided for the design and this is called the
'design hourly volume'.
• This value is to be determined from extensive
traffic volume studies

15. Environmental and other factors
• The environmental factors such as aesthetics,
landscaping, air pollution, noise pollution and
other local conditions should be given due
consideration in the design of road geometrics.
• Some of the arterial high speed highways and
expressways are designed for higher speed
standards and uninterrupted flow of vehicles
by providing controlled access and grade
separated intersections.

16. • THANKS!
• Gmail: ramkumawat001@gmail.com