Category Archives: Roads

Roads, TRANSPORTATION ENGINEERING

Camber in roads – Types of Road Cambers

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Camber in roads is the slope or angle built into the road surface, typically seen on curved or sloped sections of the road. This slope is designed to provide several benefits, including improved drainage, enhanced vehicle stability, and better driver visibility. The purpose of camber on roads is to ensure safe and comfortable driving conditions for motorists.

The slope can be positive, negative, or zero, depending on the specific requirements of the road and the expected traffic flow. The appropriate camber for a road depends on various factors, such as the type of road, its location, and the expected speed and volume of traffic. Proper design and construction of road camber can significantly improve road safety, reduce the risk of accidents, and increase the lifespan of the road surface.

  1. Types of Camber in roads
    1. Positive camber in roads
    2. Negative camber in roads
    3. Zero camber
    4. Composite camber
    5. Sloped camber/straight camber
    6. Two straight-line camber
    7. Barrel camber/Parabolic camber
  2. Significance of road camber
  3. Advantages of Camber on Roads
  4. Recommended Values of Camber in Road For Different Types of Road surface by IRC: 
  5. Disadvantages of excessive road camber

Types of Camber in roads

Camber in roads, or road camber, refers to the slope built into the road surface, typically seen on curved or sloped sections. The road’s camber is usually indicated by the ratio 1:n or as a percentage. Proper camber design and construction are crucial to improve road safety, reduce accidents, and ensure adequate drainage and vehicle stability.

Here’s a list of the types of camber used in road design and construction:

  • Positive camber
  • Negative camber
  • Zero camber
  • Composite camber
  • Sloped or straight camber
  • Two straight-line camber
  • Barrel camber

Positive camber in roads

Positive camber refers to the angle of a vehicle’s wheels where the top of the tire tilts outward from the centre of the vehicle. This can provide improved stability and handle in certain driving situations, such as high-speed cornering. However, excessive positive camber can lead to uneven tire wear and decreased handling performance.

Positive camber

Negative camber in roads

Negative refers to the angle of a vehicle’s wheels where the top of the tire tilts inward towards the centre of the vehicle. This can provide improved grip and handling during cornering, as the tire maintains more contact with the road. However, excessive negative camber can lead to uneven tire wear and reduced straight-line stability.

Negative Camber

Zero camber

Zero camber refers to the angle of a vehicle’s wheels where the tire is perpendicular to the ground and the wheel is vertical. This is considered the ideal angle for tire wear and handling, providing a balance between straight-line stability and cornering grip. Many production vehicles are designed with zero camber for optimal performance and safety.

Composite camber

Composite camber refers to a combination of positive and negative camber on a vehicle’s wheels. In order to achieve optimal handling and performance in specific driving situations, one can adjust the angle of each wheel independently to create a custom setup. This allows for a personalized approach to handling and can be achieved through the use of composite camber. Composite camber is a technique commonly utilized in high-performance vehicles and motorsports to attain maximum grip and control.

Composite Camber

Sloped camber/straight camber

Sloped camber refers to a wheel angle where the tire leans towards the inside or outside of the vehicle, creating a slope. Straight camber refers to a wheel angle where the tire is vertical and perpendicular to the ground. Sloped camber is often used in motorsports to improve cornering performance, while straight camber is more common in street vehicles for better tire wear and handling.

Straight line/ sloped

Two straight-line camber

Two straight-line camber refers to a setup where the camber angle is set to zero for both front and rear wheels. This provides a balanced setup that promotes even tire wear and stable handling. “People commonly use two straight-line camber in street vehicles, SUVs, and pickup trucks, prioritizing comfort, safety, and longevity over high-speed cornering performance.”

Two straight line Camber

Barrel camber/Parabolic camber

“In drifting and racing applications, people commonly use barrel camber to promote tire grip . This in turn improves cornering performance by adjusting the camber angle and toe settings on each wheel independently. Barrel camber is a wheel angle where the center of the tire is lower than the edges, creating a barrel-like shape.”

Barrel Camber or parabolic camber

Related posts from vincivilworld

Significance of road camber

Road engineers provide camber to promote safe and efficient driving. They use positive camber on curves and turns to offer better stability and prevent vehicles from sliding off the road. On the other hand, they use negative camber on straight sections to enhance tire traction and lower the risk of hydroplaning in wet conditions.

Advantages of Camber on Roads

Camber provides several advantages for road safety and efficiency. “Moreover,” positive camber assists vehicles in remaining centered on the road while turning. This in turn results in decreased skidding and improved stability. Negative camber improves tire contact with the road on straight sections, increasing traction and reducing hydroplaning risk. Camber also helps to reduce tire wear by distributing the load evenly across the tire surface, promoting longer tire life. Overall, camber is a key design feature in road engineering. This helps to promote safe, efficient, and sustainable transportation for all.

Road

The Indian Road Congress (IRC) provides recommended values for camber in road design, based on the type of road surface. These values are as follows:

  1. Flexible Pavement on Earth Embankment
  • Straight: 1.5%
  • Crossfall: 2.5%
  1. Flexible Pavement on Soft Soil
  • Straight: 2%
  • Crossfall: 3.5%
  1. Rigid Pavement on Earth Embankment
  • Straight: 2%
  • Crossfall: 3%
  1. Rigid Pavement on Soft Soil
  • Straight: 2.5%
  • Crossfall: 4%
  1. Bituminous Wearing Course
  • Straight: 1.5%
  • Crossfall: 2.5%

“These values provide general guidance only and depend on local conditions, traffic volume, and other factors. It is important to note that.”

Disadvantages of excessive road camber

Providing excessive road camber height can have several disadvantages. These include:

  • Uneven tyre wear: Excessive camber height can cause the tire to wear unevenly, leading to reduced tire life and increased maintenance costs.
  • Increased fuel consumption: High camber angles can increase rolling resistance and reduce fuel efficiency, leading to higher fuel consumption and greenhouse gas emissions.
  • Reduced braking performance: Excessive camber can reduce the contact area between the tire and the road surface, reducing braking performance and increasing stopping distances.
  • Reduced stability: High camber angles can reduce vehicle stability, especially at high speeds, making the vehicle more difficult to control and increasing the risk of accidents.
  • Uncomfortable ride: Excessive camber can cause the vehicle to ride harshly, transmitting more shocks and vibrations to the occupants, leading to discomfort and fatigue during long journeys.
Roads, TRANSPORTATION ENGINEERING

Bitumen for roads – Bitumen Uses, Grades and Types

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Bitumen for roads is an important topic to understand when it comes to road construction. Bitumen is used in road construction because of the wide range of features and advantages it possesses over other pavement construction materials. The significance of bitumen in the construction of roads will be demonstrated in this article. In addition, we shall see bitumen road layers, various bituminous materials, cutback bitumen, bitumen grade, and bitumen properties.

  1. Bitumen for roads – Bituminous binder types
    1. Bitumen vs Tar – Comparison
    2. Tar manufacturing
  2. Desirable properties of bitumen- an important topic in bitumen for roads
  3. Bitumen for roads – Types of Bituminous materials
    1. Cutback bitumen
    2. Bituminous emulsion
  4. Grade of bitumen for roads – Types and Uses
  5. Bitumen road layers

Bitumen for roads – Bituminous binder types

There are two types of bituminous binder for road construction.

  • Bitumen (by distillation of crude oil)
  • Tar (Produced from coal)

So, what are the difference between them?

Bitumen vs Tar – Comparison

The table below shows a comparison between tar and bitumen.

BitumenTar
Petrolium productDistillation of coal or wood
Soluble in carbon disulphide and carbon tetrachlorideSoluble in toluene only
Temperature succeptibility is lowTemperature succeptibility is higher than bitumen
Free carbon content is lessFree carbon content is more
Comparison between tar and bitumen

Now, let’s sneak into the manufacturing of tar, being one of the important bituminous materials

Related posts from vincivilworld

Tar manufacturing

Bitumen for roads - Construction in progress
Bitumen for roads – Construction in progress

Generally, tar is made by heating coal inside a chemical apparatus. Most tar is produced from coal as a byproduct of coke production, but it can also be produced from petroleum, peat or wood.

The major steps in tar manufacturing are,

  • Coal undergoes carbonation and produces crude tar
  • Crude tar undergoes distillation/ refining and produces a residue
  • The residue blends with distilled oil fraction and produces tar

I am going to tell more about the properties of bitumen now.

Also read: Classification of roads-5 types of roads full details

Desirable properties of bitumen- an important topic in bitumen for roads

Bitumen for roads - Properties
Bitumen for roads – Properties

The desirable properties of bitumen are,

  1. Viscosity of bitumen during mixing and compaction is adequate
  2. Bituminous material should not highly temperature and susceptible
  3. In presence of water the bitumen should not strip off from aggregate
  4. The adhesive property of bitumen binds together all the components without bringing about any positive or negative changes in their properties
  5. Bitumen is insoluble in water and can serve as an effective sealant
  6. Due to versatility property of Bitumen it is relatively easy to use it in many applications because of its thermoplastic property
  7. Bitumen play a vital role in distributing the traffic loads on the pavement to the layers beneath

Bitumen for roads – Types of Bituminous materials

Okay. So, what are the types of bituminous materials that are used in flexible pavement construction? Below is the list for you.

  1. Paving grade material
  2. Modified bituminous binder
  3. Cutback bitumen
  4. Bitumen emulsion

Among the list, cutback bitumen is the major. Let me tell you more details about cutback bitumen.

Cutback bitumen

Cutback bitumen is the bitumen the viscosity of which is reduced by a volatile diluent. It is used in low-temperature mixing.

Three types of cutback bitumen are available

  1. Rapid curing
  2. Medium curing
  3. Slow curing

The diluent while mixing varies with the type of cutback bitumen.

Type of cutback bitumenDiluent
Rapid curingNafthal, gasoline
Medium curingCarosine or diesel oil
Slow curingHigh boiling point gas oil
Type of cutback bitumen and suitable diluent

Bituminous emulsion

bitumen emulsion
Bitumen emulsion

A bitumen emulsion is a liquid product in which a substantial amount of bitumen suspended in a  finely divided condition in an aqueous medium and stabilized by means of one or more suitable material

Three types of bitumen emulsions are available

  1. Rapid setting
  2. Medium setting
  3. Slow setting

Also read: Alignment of road: Factors affecting- obligatory points with figures

Grade of bitumen for roads – Types and Uses

To determine the grade of bitumen, penetration test is conducted. The results are expressed in 1/10 mm. When penetration value is represented as 80/1000, it is called grading of bitumen.

The old method of grading is viscosity test. Two viscosities kinematic and absolute and penetration value by penetration test results are collected. Based on this, bitumen is graded. The tables shows the grade of bitumen and values of viscosity in accordance with penetration.

Grade of bitumenAbsolute viscosityKinematic viscosityPenetration
VG 1080025080- 100
VG 20100030060- 80
VG 30240035050- 70
VG 40320040040- 60
Grade of bitumen and viscosity

Let me tell you the application of each of the grade of bitumen now.

VG- 10- Used in spray application since viscosity is very less

VG- 20- Used in cold area

VG- 30- Commonly used in India

VG- 40- High grade bitumen used in high traffic areas

Okay. So, lets’ learn about the bituminous layers.

Bitumen road layers

Let’s first look into the road layers to understand bitumen road layers.

bitumen road layers
bitumen road layers

The bitumen road layers come in the surface layer shown in the figure above. The figure below shows that. Bituminous mix consists of aggregate and binder. Aggregate consists of coarse aggregate, fine aggregate and filler less than 0.075mm.

Bitumen road layers
Bitumen road layers
  • Bituminous concrete consists of aggregate and bitumen.
  • Thickness of base course depends on grading of aggregate
  • Dense graded aggregates are provided in base course. That is the permeability will be very less
  • Number of voids should be very less
  • Dense bituminous macadam should be given as a binder course

So, the trip is over. Hope the time you spend for reading about the bitumen for road was worth it.

MUST READ: Road margins- 6 types of road margin in highway

Happy learning!

Roads, TRANSPORTATION ENGINEERING

Bitumen Softening Point Test – Ring and ball method

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The bitumen softening Point Test is done to determine the consistency of bitumen. Bitumen is a viscoelastic material, which means it behaves like both a liquid and a solid state. It does not have a specific melting point. As the temperature increases, the bitumen becomes softer and the viscosity of the bitumen decreases. One of the common parameters for classifying bitumen is the softening point of the bitumen. This property shows at what temperature the bitumen softens. 

Bitumen Softening Point Test

Bitumen softening point is measured in different ways such as:

  • Ring and Ball Method (R&B)
  • Krämer-Sarnow Method (KS)
  • Mettler Softening Point Method
  • Capillary Method
  • Flow Point Method
  • Drop Point Method

The ring and Ball method is the most frequently used to determine the softening point of bitumen.

Bitumen roads
Bitumen roads

Why Is The Bitumen Softening Point Important?

To pave the roads and aeroplane runways, it is necessary to use a type of bitumen that has a specific degree of softness. Choosing a suitable bitumen with a good softening point depends on the weather condition and traffic loads.

For example, if the average temperature in a region is high during a year, bitumen with a    higher softening point should be used to make asphalt pavement. If during the year, the number of vehicles crossing this road is high and they put a  lot of pressure on the road surface, more bitumen should be used in the asphalt. This work increases the strength of the asphalt.

Related posts – Bitumen

International Standard Methods of softening point test

The softening point  test  of  bitumen  is  in  the  accordance   with  the following standards:

  • ASTM D36
  • ASTM E28-67/E28-99
  • ASTM D6493 – 11
  • IS 1205
  • EN 1427
  • IP 58
  • ISO 4625
  • JIS K 6863

The most common standard method for determining the softening point of bitumen is ASTM D36, which we will discuss further. You can see the steps of the Ring and ball method through the Video produced by the Infinity Galaxy team.

Softening point test of bitumen – Ring and ball method (Video)

YouTube video
Youtube video

Softening Point Test Procedure

The ring and ball method is widely used to determine the softening point of bitumen. In  the  infographic  below, you  can  see  a  summary  of  the  bitumen softening point test:

Softening point test procedure
Softening point test procedure

The required equipment to do the bitumen softening point test are:

  • Two steel balls
  • Two brass rings
  • Beaker
  • Thermometer
  • Heater
  • Knife
  • A glass surface 
  • Bitumen
  • The bases holding the rings

Bitumen Softening Point Test Steps:

  • In the first step, it is necessary to prepare the test sample. Heat the bitumen to a   temperature between  75  and 100 °C. Stir the bitumen well until it becomes completely liquid and free of air and water bubbles. Heat the rings to the approximate temperature of the bitumen. Prepare a mixture of glycerin and dextrin in equal proportions.
  • Cover the surface of the metal or glass plate with it. Pour the heated bitumen into the rings to fill them. After cooling in the air, it is necessary to draw the extra bitumen with a heated knife at an angle of 45 degrees on the surface of the rings. So far you have understood how to prepare the sample.  In the following, we will explain the process of conducting this test.
  • Place the rings filled with bitumen on the bases and place them in a water bath with a temperature of 5 °C for 15 minutes. Cool the steel balls to a temperature of 5 °C. Put them in the beaker and fill them with distilled water up to about 50 mm above the rings. Now place the steel ball in the centre of the ring and tangent to the bitumen and heat it until the temperature rises 5±0.5 °C/min.

Ring and ball method – Results

  • As the temperature increases, the bituminous material softens and the balls sink through the rings. Continue heating until the balls on the bitumen reach the surface of the metal blade under the rings and note the temperature when each of the balls contacts the bottom of the plate. Consider the average of the two temperatures obtained as the bitumen softening point.
  • An important point in this experiment is the process of heating the beaker and its contents, i.e. bitumen.   Since this test is very sensitive to heat, it is necessary to use the same heating rate throughout the test. It should be noted that if the bitumen is blown and hard, glycerin liquid is used instead of water.

Roads, TRANSPORTATION ENGINEERING

Penetration Test for Bitumen – Significance and Procedure

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The penetration test for bitumen is a laboratory method for grading bitumen based on its hardness. In this test, the amount of penetrating a specific needle into the bitumen is measured.

More than 85% of bitumen is used in road construction. Weather condition affects on bitumen binder. In cold weather, bitumen becomes hard, and the possibility of cracking increases. On the other hand, hot weather causes bitumen becomes soft and sticky.

Both situations are not acceptable as a result of civil engineers using penetration tests.

What is the Penetration Test of Bitumen?

The penetration test for bitumen is a laboratory method for grading bitumen based on its hardness. In this test, the amount of penetrating a specific needle into the bitumen is measured.

This value is reported in a tenth of a millimetre or Deci-millimeter (DMM) as a penetration value. The penetration test can be used for refinery bitumen, emulsion bitumen, and oxidized bitumen. Based on this test bitumen is classified into penetration grades of 20/30, 30/40, 40/50, 50/60, 60/70, and 80/100.

This test can measure the penetration value in the range of 20 to 300 dcmm. It can recognize the bitumen consistency and stability of bitumen.

Let’s see this test history and application.

The Bitumen Penetration Test History

The first uses of the penetration test, date back to the early 19th century. Before that, the hardness of bitumen is measured based on the Chewing test. It was a completely experienced test. Through that, an engineer chews a moderate-temperature bitumen sample. Then reports the hardness of bitumen according to the difficulty of chewing. Because of the chewing test’s inaccuracy, the penetration test was introduced to the industry. 

An overview of the Bitumen Penetration test Importance

More than 85% of bitumen is used in road construction. Weather condition affects on bitumen binder. In cold weather, bitumen becomes hard, and the possibility of cracking increases. On the other hand, hot weather causes bitumen becomes soft and sticky. Both situations are not acceptable as a result of civil engineers using penetration tests.

Bitumen with high penetration values is suitable for cold weather. Because it does not harden and crack when exposed to low temperatures. On other hand, bitumen with smaller penetration values is suitable for hot weather. Because high temperatures can not soften it. Most workable penetration bitumens are penetration grades 60/70 and 80/100. Penetration grade 60/70 can apply to road construction in warm weather and 80/100 is suitable for cold weather.

Bitumen penetration grade 80/100 means that the needle penetrates into the bitumen in the range of 80 to 100 decimeters.

How Is the Penetration Test of Bitumen Performed?

In the following, you can familiarise yourself with the apparatus and the procedure of the test based on ASTM D5. Before that watch the below video by Infinity Galaxy which introduces the penetration test of bitumen.

r

 Apparatus

  • Penetrometer 
  • Container
  • Water bath
  • Stopwatch
  • Thermometer
penetrometer

Procedure 

In the first step, bitumen should be heated up until it becomes liquid. Bitumen should not be heated in a temperature range above 90-100 degrees Celsius otherwise it will burn. While the temperature rises, stir the bitumen to make sure it is uniform. Bitumen should also be free of water and air bubbles.

In the next step, pour the melted bitumen into the container and let it cool at room temperature. 

After that put the bitumen container in the water bath with a constant temperature of 25 degrees Celsius and let the sample reach the same temperature.

Then place the container under the penetrometer. Move down the needle just above the bitumen surface. 

Thereafter, apply the needle which has a 100gr load just for 5 seconds. Repeat the test 3 times and write down the results each time. The needle tip in each repetition should be apart 10mm from the previous measurements.

Report the mean value as the penetration value of the bitumen sample. The following picture is other important bitumen tests in road construction:

Infographics – 10 Major bitumen tests

Roads, TRANSPORTATION ENGINEERING

Highway Engineering- Definition, Importance and Construction Details

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Highway engineering is an important topic in civil engineering. It includes the study of roads in depth. The technical aspects involved in this subject plays a significant role in construction of different types of roads. In this blog, I will show you all the details of the subject including the definition, topics, importance etc.

Let’s start from scratch.

What is Highway Engineering

Highway engineering is a subset of highway engineering that deals with the planning, development, and upkeep of various types of roads, tunnels and bridges. It plays an important role in ensuring safe and efficient transport of people and goods. It entails researching the following topics:

1) Highway planning, location, and growth.

2) The materials needed to build a highway.

3) The performance of highway traffic and its regulation.

4) Road drainage, etc.

Before we jump on to the details, let me tell you the importance of highway engineering.

Importance of Highway Engineering

Highways top view
Highways top view

The Importance of roads is summarised below.

1. They provide transportation for people, commodities, raw materials, and other items to various parts of the world.

2. In hilly areas, they are the only means of contact.

4. Assists in the upkeep of law and order in a government.

Let’s talk a bit about the planning of highways in the next section.

Planning and Development of Highway Engineering

The prediction of existing and potential traffic volumes on a road network is part of highway planning.

Highway planning is also a fundamental requirement for highway construction. Highway engineers work hard to anticipate and assess all potential civil consequences of highway systems.

The negative effects on the environment, such as noise pollution, air pollution, water pollution, and other ecological impacts, are among the factors to consider.

What are Highway plans?

In highway engineering, Highway plans or Highway drawings are drawings created from data obtained during various surveys conducted for the purpose of locating a highway.

The main map, index map, preliminary survey plans, and other plans or sketches prepared in connection with a road project are examples. On separate papers, the specifics of additional works such as bridges, culverts, railway crossings, and so on are planned.

Purposes and Objectives of Highway Plan

1) To discover how the highway works.

2) To estimate the cost of the road project.

Its time to know about the construction.

Construction of highways

Newly constructed highways
Newly constructed highways

In most cases, extensive surveys and subgrade planning precede highway construction. There are many aspects of highway design that can be broken down into technological and commercial components.

The following are some examples of each:

Elements of technology

  • Material quality
  • Installation techniques
  • Traffic

Commercial elements 

  • Environmental considerations in contracts
  • Aspects of politics and law
  • Concerns from the public

Regardless of the project type, highway construction usually starts at the lowest elevation of the site and progresses upward. By looking over the project’s geotechnical requirements, we get an idea about the following:

  • Current ground condition.
  • Specific equipment requirement for excavation, grading, and material transportation to and from the site.
  • Properties of material to be excavated.
  • For below-grade work, dewatering requirement.
  • Excavation safety criteria
  • Quantities of water for dust control and compaction

How about the maintenance of highways? I will show you in the next section.

Maintenance of highways

The ultimate goal of highway maintenance is to correct flaws and maintain the structure and usability of the pavement. In order to construct an adequate maintenance plan, defects must be identified, recognised, and registered. Flexible and rigid pavements have different defects.

The four primary goals of highway maintenance are as follows:

  1. Repairing functional pavement defects helps to prolong the pavement’s functional and structural life. 
  2. Ensure road protection and signage.
  3. Keep the highway in a usable state
  4. Highway systems and all of their components can be kept in initial, as-built condition by following routine maintenance procedures.

Last, but not the least a bit about the safety.

Highway Engineering Safety

Highway engineering safety is important since it involves the life of people. Automated traffic signals can be used to further ensure this.

Highway under construction
Highway under construction
  • Safety management is a comprehensive approach to reducing the frequency and severity of traffic incidents. 
  • The key to improving highway safety is to design, develop, and maintain highway structures that are much more tolerant of the average range of man/machine interactions with highways. 
  • Over time, technological advances in highway engineering have enhanced the methods used in design, construction, and maintenance.

That’s it. Let me know if you need any further details.

Happy learning!

Roads, TRANSPORTATION ENGINEERING

Cloverleaf interchange- Examples and Problems

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The cloverleaf interchange is one of the attractive innovations in civil engineering. A cloverleaf interchange is a two-level interchange at which left turns are done by ramp roads (reverse directions in left-driving regions). It is not only aesthetically pleasing but also provides several advantages to the transportation system.

We will go through the main details in the blog.

Let’s start from scratch.

  1. What is cloverleaf interchange ?
  2. Examples of cloverleaf interchange in India
  3. Cloverleaf interchanges – Main problems and challenges
  4. Upgrades for cloverleaf interchanges
  5. Traffic signals in leu of cloverleaf interchange

What is cloverleaf interchange ?

Clover leaf interchange example
Clover leaf interchange example
  • A cloverleaf interchange is a two-level interchange at which left turns are done by ramp roads (reverse directions in left-driving regions).
  • Vehicles first proceed to go left (in right-hand traffic) as one lane crosses over or below the other. Then, exit right onto a one-way three-fourth loop ramp (270 °) and merge onto the intersecting road.
  • The purpose of a cloverleaf is to allow two highways to cross without the need for any traffic to be stopped by red lights, except for the left and right turns.
  • Traffic weaving is the limiting factor in a cloverleaf interchange’s ability.

In the next section, let me take you through some examples of clover leaf in India.

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Examples of cloverleaf interchange in India

Clover leaf interchange
Clover leaf interchange
  1. Kathipara Cloverleaf, Chennai
  2. Maduravoyal Cloverleaf, Chennai
  3. Koyambedu Cloverleaf, Chennai
  4. Badarpur Cloverleaf, Delhi
  5. Yamuna Cloverleaf-Noida
  6. Mukarba Chowk Cloverleaf, Delhi
  7. BMIC Cloverleaf, Karnataka

Also read: Road pavement structure-Components and functions

So, you got an idea about clover leaf roads. Let me quickly walk you through the major challenges and problems associated with this.

Cloverleaf interchanges – Main problems and challenges

Clover leaf interchange top view
Clover leaf interchange top view
  • The biggest downside of the cloverleaf’s classic configuration is that at the end of a loop, vehicles converge on the highway immediately before other vehicles exit to go around another loop, causing a dispute known as weaving.
  • Weaving restricts the number of traffic-turning lanes.
  • Since then, the majority of road authorities have adopted new interchange designs with less-curved exit ramps which do not lead to weaving.
  • These interchanges include diamond, parclo and single-point urban interchanges (SPUI) when connecting at the crossroads to an arterial road in non-free-flowing traffic and the stack or clover and stack hybrids when connecting in free-flowing traffic to another freeway or to a busy arterial where signals are not yet needed.

Upgrades for cloverleaf interchanges

  • For new interchanges, not only are these ideas valid, but they also hold when existing cloverleaf interchanges are upgraded.
  • The exchange between US 13 and US 58 was originally a cloverleaf in Norfolk, Virginia; it has since been turned into a SPUI.
  • In addition, several cloverleaf interchanges are being upgraded to parclos on California freeways, such as U.S. 101. In Hampton, Virginia, a cloverleaf interchange was partly unwound into a partial stack interchange between Interstate 64 and Mercury Boulevard.
  • As part of a major highway improvement project to upgrade the highway to Interstate standards, four cloverleaf interchanges along I-64/US 40 in St. Louis, Missouri, were substituted with SPUIs between 2008 and 2009.
  • Adding a collector/distributor route next to the highway is a compromise; this does not prevent weaving but takes it off the main lanes of the freeway. An example of this is the Sheboygan, Wisconsin, State Highway 23/Interstate 43 interchange, where the exit/entrance roads on and off Highway 23 are two lanes on the north and southbound sides of the road next to the main I-43 freeway.

Traffic signals in leu of cloverleaf interchange

  • Several cloverleaf interchanges on the non-freeway route have been removed by installing traffic signals.
  • This is also done sometimes at the intersection of two freeways, particularly when one freeway ends at an interchange with another.
  • An example of this is at the intersection between Interstate 5 and Washington State Route 512 in Lakewood, Washington, where a noticeable ramp stub reveals that one of the four leaves has been cut, thus removing weaving on I-5.
  • The traffic signal will be replaced by a two-lane flyover in the future, again completing the freeway-to-freeway interchange.
  • Cloverleaf exchanges often appear to consume much more land than any other form of exchange (with the possible exception of stack interchanges).
  • Numerous cloverleaf intersections include the merging of traffic from the clover directly into the collector/distributor lane in the Lower Mainland of British Columbia, Canada.
  • This allows the slowly moving driver to merge around the loop ramp with the rapidly moving driver leaving the collector/distributor lane without the ability to accelerate to balance the oncoming driver’s flow.
  • This merging velocity gap can be as high as 65 km/h (approx. 43 mph).
  • In the United Kingdom, owing to these performance concerns, the cloverleaf interchange was not introduced in significant numbers. Originally, there were three, one in Redditch and two in Livingston.
  • In Ontario, most cloverleaf interchanges have been phased out, but with similar traffic patterns, some near variants remain.
  • However, the key difference is that single bidirectional carriageways share the adjacent on and off-ramps.
  • Examples include the intersection in Belleville, Ontario, between Highway 62 and Highway 401, as well as the interchange in Toronto between Lawrence Avenue and Don Valley Parkway.

So, how was the trip through the clover leaf interchange? Let me know in comments, if you have any queries.