Length Of Transition Curve

In this article, I will show you how to design the length of the transition curve or, how to calculate or, determine the length of the transition curve.

The length of the transition curve is designed to fulfil the three conditions as mentioned below. The length of the transition curve for design should be the highest of the three values.

1. The Rate of Change of Centrifugal Acceleration

The rate of change of centrifugal acceleration is to be developed gradually. From this consideration the length transition curve is given by the following equation:

Ls = 0.0215 V³/ CR

Where, Ls = Length of transition curve in m, V = Speed of vehicle in Km/h, C = Rate of change of centrifugal acceleration, R = Radius of the circular curve in m.

The minimum and maximum values of C are limited to 0.5 & 0.8 respectively.

2. The Rate of Introduction of Designed Super Elevation 

The rate of introduction of designed superelevation is to be at a reasonable rate. From this consideration, the length of the transition curve is given by the following :

Ls = e.N (W + We)/2

Where, e = The rate of designed superelevation, W = Normal pavement width in m, We = Extra widening pavement at the circular curve in m. 1/N = Rate of change of superelevation (Minimum value of N is 150 to 60 ). 

3. By Empirical Formula

According to I.R.C standards, the length of the horizontal transition curve should act, then the value given by the following equations:

a)For plain and rolling terrain

Ls = 2.7 V²/R

b)For mountainous and steep terrain

Ls = V²/R

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Length of Valley Curve

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Recommended Gradient As per IRC

Recommended gradient as per I.R.C for plain terrain, mountainous terrain, and steep terrain:

1. Plain or Rolling Terrain

Ruling gradient:- 1 in 30 (3.3%).
Limiting gradient:- 1 in 20 (5%).
Exceptional gradient:- 1 in 15 (6.7%).

2. Mountainous Terrain

Ruling gradient:- 1 in 20 (5%).
Limiting gradient:- 1 in 16.7 (6%).
Exceptional gradient:- 1 in 14.3 (7%).

3. Steep Terrain

Ruling gradient:- 1 in 16.7 (6%).
Limiting gradient:- 1 in 14.3 (7%).
Exceptional gradient:- 1 in 12.5 (8%).

Note: The maximum gradient at hairpin bend shall be 2.5 % for mountainous and steep areas.

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Types of Gradient

 Recommended Roadway Width, Shoulder, Carriageway Width As Per I.R.C

Recommended Standards For Building line & Control line For Plain & Rolling Area

Classification of Road

Traffic Control Devices

The various aids and devices used to control, regulate and guide traffic are known as traffic control devices. The commonly used traffic control devices are:

• Traffic signs or road signs.
• Traffic marking or road marking.
• Traffic island.

The main object of providing traffic control devices on road is to provide safe, convenient and economical transportation of persons and goods.

Basic Requirements of Traffic Control Devices

The traffic control devices must meet the following basic requirements: 

1. It should provide a good visual guide to road users.

2. It should provide timely warning of the hazardous situation other important information.

3. It should not involve heavy maintenance expenditure.

4. It should involve a low initial cost.

5. It should have an aesthetically pleasing experience.

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Traffic Rotary

Advantages and Disadvantage of Traffic Signal

8 Purpose of Traffic Volume Survey Study

Following are the 8 purposes of traffic volume survey Study:

1. To establish the relative importance of any route or road facility.
2. To plan and design the existing and new facilities of traffic operations on the road.

3. To decide the priority for improvement and expansion of a road and to allow the funds accordingly.
4. To make an analysis of traffic patterns and trends on the road.

5. To do the structural design of pavements and geometrical design of roads by classified traffic volume study.
6. To plan one-way street and other regulatory measures by volume distribution study.

7. To do the design of road intersections, planning signal timings.
8. To do the planning of sidewalks, crosswalks and pedestrian signals.

Traffic Rotary

A traffic rotary or rotary intersection or say a roundabout is a specialized form of road intersection at grade, where all converging vehicles are forced to move around a large central island (Rotary Island) in one direction (clockwise direction) before they can weave out of traffic flow into their desired direction.

The main objectives of providing a rotary are to eliminate the necessity of stopping for crossing streams of vehicles and to reduce the area of conflict.

Advantages of Traffic Rotary

The advantages of providing a traffic rotary(Roundabout) are as follows:

1. Orderly and disciplined traffic flow is provided by the one-way movement.
2. Frequent stopping and starting of vehicles are avoided.

3. Direct conflict is eliminated.
4. All turns can be made with ease.

5. A rotary is especially suited for intersection legs ranging from 4 to 7.
6. For moderate traffic, rotaries are self-governing and need no control by police or traffic signals.

7. The capacity of rotary intersection is the highest of all other intersections at grade.

Disadvantages of Traffic Rotary

The disadvantages of providing traffic rotary(Roundabout) are as follows:

1. Rotary requires comparatively large of land. So where space is limited and costly, the total cost may be high.  

2. Where pedestrian traffic is large, the rotary by itself cannot control the traffic and needs control by traffic police. If the vehicular traffic has to stop to allow the pedestrian to cross, the main purpose of rotary has defected.

3. At places of mixed traffic, the design of the rotary becomes too elaborate and the operation and control of traffic become complex.

4. Where the angle of intersection of two roads is too acute or when there are more than seven intersecting roads, rotaries are unsuitable.  

5. When the distance between the intersections on important highways is less, a rotary becomes troublesome.   

6. At places of mixed traffic, there is a tendency to break the traffic regulation of clockwise movement.  

7. Where the traffic volume is very low, the construction of a rotary cannot be justified.

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Traffic Signs

 Grade Separated Intersection and Their Advantages and Disadvantages & Classification

Refuge Island or Channelizing Island And Their Purpose

Grade Separated Intersection

The road intersections where all the roads join or cross at a different level by providing a bridge (over bridge or underpass), is called grade-separated intersection. 

Classification of Grade Separated Intersection

The various grade separated intersection are classified into the following two categories.

1. Overpasses 
2. Underpasses

Over Passes

When the major Highway is taken above by rising its profile above the general ground level by an embankment and an overbridge across another highway, it is called an overpass. Cloverleaf pattern fly-over, trumpet-type fly-over is the example of overpasses.

Under Passes

When the highway is taken by it depressing it below the ground level to cross another road by means of another bridge, it is called an underpass.

Advantages of Grade Separator

The advantages of providing grade separator are as follows:

⇛ Grade separator provides maximum facility to the crossing traffic and avoids the accident while crossing.

⇛They provide increased safety for turning traffic. By introducing indirect interchange ramp, even right turn movements can be made quite easy and safe.

⇛ Grade separation is an essential part of controlled access highway like an expressway.

⇛ It is possible to adopt grade separation for all likely angles and layout of intersecting roads.

⇛ Stage construction of additional ramps is possible after the grade separation structure between main roads is construction.

⇛ Traffic capacity is increased.

Disadvantages of Grade Separator 

The disadvantages of providing grade separator are as follows:

⇛ The construction cost is very high.

⇛ Construction of grade separator is costly, difficult and undesirable where there is limited right of way or where the topography is not favourable.

⇛ In flat or plain terrains, grade separation may introduce undesirable crests and sags in the vertical alignment.

Read Also: 

Traffic Rotary and Their Advantages and Disadvantages

Refuge Island or Channelizing Island And Their Purpose

Kerbs

What is Kerbs?
Kerbs are the component of a city road. A kerb also termed as a curb is a vertical or sloping member provided along the edge of a pavement or Shoulder to give strength and protect the edge of the pavement. 

The meaning of kerbs or curbs is a barrier or boundary. However, in highway engineering, it indicates the boundary between the pavement and shoulder or sometimes island or footpath or car parking space.  

kerbs are generally constructed of cut stone or cement concrete slabs. The kerb and the road surface near the edge together from a side channel which carries rainwater that comes from the road surface.

4 Types of Kerbs

Kerb is the boundary between the pavement and shoulder or footpath. kerb may be divided into four groups based on their functions.  

Following are the 4 types of kerbs are used in the roads:

(a) Low or Mountable Kerbs

This is also known as class I kerb. Its principal role is to control traffic to stay within its own lane. As the height of this form of kerb is low, it facilitates the driver to enter the area of the shoulder with less difficulty.   

This type of kerb is also beneficial for the longitudinal drainage system. The height of this type of kerbs is 70 to 80 mm. 

(b) Low-Speed Barrier or Urban Parking Kerb 

This is also known as Class II kerb. It prevents encroachment of slow speed or parking vehicles to the footpath. However, with severe emergency vehicles, they can climb and be parked on footpath or shoulder.  

The height of this type of kerb is 150 to 200 mm with a batter of 25 mm to avoid the scraping of tyres.

3. High-Speed Barrier Kerbs 

This is also known as Class III kerb. It is usually used in critical places such as bridges or mountain roads, This type of kerbs are 230 to 450 mm or more in height.  

4. Submerged Kerbs

Submerged kerbs are provided in rural roads at pavement edges between the edge and shoulders. It is provided in the form of standing bricks or concrete blocks.  

It offers lateral stability to the granular base course and flexible pavements.

What are the uses of road kerbs?

Curbs or kerbs are provided for the following purposes:

1. This prevents the vehicle from parking beside the road.

2. It acts as a boundary between the pavement and the footpath.

3. Kerbs provide structural support for the pavement.

4. It helps to overcome slipping risk of the vehicles.

5. It helps to reduce the number of accidents.

6. It is also used for drainage purposes.

Read Also: 

5 Components of a City Road-Footpath, Kerbs, Pedestrian Crossing, Traffic lane, Median

Types of Roads 

Spoil Bank

Lead and Lift  in Earthwork

Turfing in Earthwork Embankment