Project 1 - Geometric Design Parameter- Prerequisites

Q.List all the highway elements required for Road Geometric Design as prerequisite & necessary checklist during design. eg. Design Speed, Design Vehicle etc..

Ans: As a Geometric Road Design depends on various factors and each and every factor palys a major rolein design of a good and safe Highway.

• Geometry control factors
• Design Speed
• Topography
• Design vehicle
• Traffic
• Eccconomy
• Environment
• Human
• Aesthetics

Geometry control factors:

Inputs: Safety & Mobility for all the public, Economic sustainability, Environmental sustainability.

Outputs: Design Speed,Design hour, Design Vehicle, Design year.

Design Speed:

Design speed is most important of Geometry control factors.It is directly linked to sight distance, Horizontal curve & Vertical Curve.

The Speed of a Vehicle vary with respect to type of vehicle,Driver,Terrain Condition.

As we know that speed varies to different vehicles & Drivers, but the design speed should satisfy all the vehicles and driver types based on terrian conditions also.

Here comes the Percentile for National Highways & State Highways, Major District Roads, Other District Roads, Village Roads .

For above different roads the areas also differs as the conditions too like Plain Area, Roling Area, Hilly Area, Steep .

Topography:

It is a 3D representation of Surface features of the land (x,y,z).Topography can impact the other factors like Design speed,cost etc..

Plain terrain : Area of the country having cross slope varying from 0-10%.

Rolling terrain : 10-25%

Hilly : 25-60%

Steep terrain : >60%.

Design Vehicle:

Normally Design vehicle consists of standard weight, dimensions, height limits and other operating characterstics.

Generally the Height limits under 5.5m,Dimensions,Weight of vehicle, influence gradient, turning radius, width of carriageway, clearance requirements and other geometric features these are all considered.

Normally we have 3 types of commercial vehicles:

Single Unit

Semi Trailer

Truck Trailer , where the selection depends upon terrain conditions, economic justification & importance of road.

There are some Axle's also like Front axle, Rear, Tandem (which is fitted with 8tyres)etc..

Traffic:

Normally for peak traffic flow it will be unfair and un economical to the design road.

We should conduct a traffic survey for 7/24hr count either in manual count or video graphic count.

AADT - stands for Annual Average Daily Traffic

PCU - Passenger Car Unit

Economy:

The economy always a majorrole in deciding the Geometry.

The road designs are to be economical as far as possible.

It should match with in the budget or funds planned including the other costs like maintance & all.

Environment:

There will be some Zones like school zone, Forest area, Noise restricted zones where we should provide the road straight and visibility should be clear.

we should not provide too many curves in that areas and road signs must be incicated before 10-15 m.

Human:

As a road user human behaves like driver,pedestrain,cyclying etc..need to be considered.

The reaction time of the driver behaviour & mental conditions , pedestrains crossing the roads these all influence the Geometry.

There is a theory named PIEV theory that reflects the reaction time of driver in b/w 2.5-5sec or 0-0.5sec.

Aesthetics:

There will be so many Tourists placeshistorical buildings , like natural ones which comes in to considerations. there should be nothing damages during the roads & designing them we should carefully handle them.

Arboric culture means the plantation along the roads it reduces noise pollution, air polllution, keeps the stretch with high Oxygen etc..

There are so many else to be considered while Designing they are:

• Cross-Section
• Sight Distance
• Horizontal Design
• Superelevation
• Extra widening
• Gradient
• Vertical curve

Combinelly we can give the 3D layout for a Highway.

Cross-Section:

Generally it varies from place to place like necissity of side walk will be provided @ built up area but no need in open terrain.

Closed drain will be provided in Urban areas where as the open trapizodial or triangular drains will be in open terrains, and also like this there are many elements that should be considered they are:

• Camber
• Width of Carriageway
• Kerbs
• Friction
• Light reflection
• Drainages
• Unevenness
• Road Margins
• Shoulders
• Medians
• Bus bay/Truck bay all should be considerd as per IRC standards.

Sight Distance:

The actual distance along the road with which the driver can see from specified height above the carriageway has a visibility.

SSD,OSD,ISD,HSD,SSD these are the types of sightdistances Stopping Sight Distance, Overtaking,Intermediate,Headlight&Safe .

There is a theory PIEV theory

P-Perception,I-Intellection,E-Emotion,V-Volition.

there are so many in these to be considered like

Speed of vehicle

Efficiency of breaks

Frictional resistance

Spacing b/w vehicles

Gradient of road

Acceleration rate of overtaking vehicles

Reaction of driver, these all shouldbe considered from various sight distances.

Horizontal Design:

The alignment is a route of road with curves like we say Horizontal curve,horizontal tangents etc..,The change in alignment direction is often necessary due to restructions imposed by

Topography,Environment & ecological qualities of area,Presence of Old Historic monuments,Sites of Structures,Availability of land,Horizontal alignment design is also very important to prevent from accidents.

Factors that effect the road design during the horizontal curve are:

Terrain,vehicle characterstics,Driver limitations,Design Speed, SightDistance, Drainage Conditions,Economy,Environment.

Types of Horizontal curves:

Simple Curve, Compound Curve, Reverse Curve, Spiral Curve.

there is Degree of curve which of 2 types: (Arc def),(Chord def).

Superelevation:

The centrifugal force is counteracted by superelevation & friction a slite inward tilt is provided to avoid skidding is known as superelevation.

By this we have Minium curve radius also it is necessary for smooth curves.

ExtraWidening:

Normally a curve can take place anywhere but for that curve we should provide Transition curve Extrawidening for the radius we have there.

There are 2 types : Mechanical widening, Psychological widening.

Transition curve:It is the curve which is provided b/w Straight line & curve line,there will be variable radius which is from tangent zero.

Types of Transition :Lemniscate, Cubic parabola, Spiral.

Gradient:

The rate of rose or fall along the length of road with respect to horizontal curve termed as gradient .

Types of gradient: Design ,Limiting,Exceptional,Minimum.

Vertical Curve:

Considerable forces are developed when the vehicle changes from one grade to another grade,this creates a discomfort to driver,so to avoid this we use vertical curve.

Types of Vertical:Summit curve, Sag curve.

Necessary check list are:

• Basic Design Criteria

Like Design speed,Design period,Design vehicle, pedestrains facilities,etc..

• Geometric Design Creteria

Like Vertical alignment,Horizontal alignment,Superelevation,Cross section, Inersection,utilities etc..