1. Importance of Geometric Design

2. Importance of Geometric Design
The geometric design of a highway deals with the dimensions and layout of visible features of the highway such as alignment, sight distance and intersection.

3. Optimum efficiency- Maximum safety- Reasonable cost
The geometrics of highway should be designed to provide optimum efficiency in traffic operations with maximum safety at reasonable cost.
The designer may be exposed to either planning of new highway network or improvement of existing highways to meet the requirements of the existing and anticipated traffic.
2500
2015
12500
2035
PCU/day
Year

4. Improving Geometric Elements in Stages
Improving in stages is very difficult and more expensive
Design geometric features at the initial stage itself considering future traffic scenario
For example, in 2015 the road may be designed for 80 kmph. But the designer has to consider for 120 kmph as the road may be upgraded in future. Accordingly Sight distance, super-elevation etc are to be designed.

5. Elements of Geometric Design of Highways
Width of pavement
Cross section elements
Formation and land
Surface characteristics
Cross slope of pavement
SD available in horizontal curve
Sight distance consideration
SD available in Vertical curve
SD available at intersections
Horizontal alignment details
Super-elevation
Transition curves
Vertical alignment details
Intersection elements

6. Design control criteria

7. Design Factors
The geometric design of highways depends on several design factors which control the geometric elements are:
Design Speed
Topography
Traffic Factors
Design hourly volume and capacity
Environmental and other factors

8. Design Speed Most important factor
Decided based on overall requirement of highway
In India depends on category of road design speed assigned (NH/SH/MDR/ODR/VR)
Design speed varies with topography

9. Design Speed Every geometric elements depends on speed For example,
Pavement surface characteristics
Width & side clearance
Sight distance requirements
Radius of curve
Super-elevation
Summit or valley curve

10. Topography Design Speed of NH/SH 100 Kmph Plain Terrain 80 Kmph
Rolling Terrain
Mountainous Terrain
100 Kmph
80 Kmph
50 Kmph
Design Speed of NH/SH

11. Traffic Factors
Different vehicles have different characteristics like height, weight, braking nature etc.

12. Design Hourly Volume Flow fluctuate with time Off-peak versus Peak
Uneconomical to design for PH traffic
Reasonable traffic value called design hourly volume
DHV for urban 8-10% ; for rural 12-18%

13. Environmental & Others
Factors such as aesthetics, landscaping, noise pollution and other local conditions should be given due consideration in the design of road geometrics
Grade-separated intersection for expressways to achieve higher speed standards