Highway Geometrics- (Camber, Land Width, Carriage way, Sight Distance, Super Elevation, Gradient)

Highway Geometrics is a branch of highway engineering that focuses on the physical and geometrical elements of roadways. This includes:

• Land width

• Formation width

• Carriageway

• Side slopes

• Shoulders

• Kerbs

• Sight distance

• Superelevation

• Highway curves

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1. Land Width

Land width refers to the total width of land acquired by the government for the construction and maintenance of a roadway. No public buildings are permitted within this land boundary.

Factors affecting land width:

• Type of road: Higher-category roads like National Highways (NH) require more width than lower-category roads.

• Future traffic growth: Consideration is given to expected increases in traffic and economic or industrial development along the route.

• 

  Carriageway and formation width

2. Carriageway

The carriageway is the paved central portion of the road used by vehicles for travel. It is surfaced with materials like bituminous concrete to ensure durability and comfort for users.

• The width of the carriageway depends on the number of lanes, which is determined by the class of the road.
  Example: National Highways typically have multiple lanes, resulting in a wider carriageway.

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3. Camber

Camber is the transverse slope provided to the road surface to facilitate the drainage of rainwater, thereby improving the road’s performance.

It is denoted as:

• 1 in n or

• x% slope

Functions of Camber:

1. To maintain a safe friction between the road surface and tires.

2. To preserve the strength and durability of the road surface.

3. To protect the subgrade soil from water infiltration.

Types of Camber:

• (a) Straight Camber: Formed by two straight surfaces meeting at the crown (the central, highest point of the road). Rarely used due to edge discomfort.

• (b) Parabolic Camber: Features a continuous parabolic curve. Also uncommon due to steep edge slopes creating outward thrust.

• (c) Mixed Camber: Combines a parabolic center with straight edges, resolving the issues of both previous types. This is the most commonly used camber type in road construction.

Types of Camber

4. Gradient

The gradient is the longitudinal slope provided along the road to establish vertical alignment.

Types of Gradient:

• (a) Ruling Gradient: The design gradient, used under normal conditions.

• (b) Limiting Gradient: Used when terrain or conditions prevent use of the ruling gradient.

• (c) Exceptional Gradient: Used only in rare or emergency cases for short distances.

• (d) Minimum Gradient: Required in flat areas to ensure proper drainage.

A vehicle on ascending gradient

5. Sight Distance

Sight distance is the length of road visible to a driver at any moment. It is measured from a driver's eye height of 1.2 m, ensuring visibility of an obstacle of 0.15 m height, as standardized by the Indian Roads Congress (IRC).

Types of Sight Distances:

• (a) Stopping Sight Distance (SSD):
  The minimum distance required to bring a vehicle to a complete stop from the design speed without hitting an obstruction.
  → Also called the absolute minimum sight distance.
  → Provided at all road sections.

• (b) Overtaking Sight Distance (OSD):
  The distance needed for a vehicle traveling at design speed to safely overtake a slower-moving vehicle without colliding with oncoming traffic.
  → Usually provided at selected locations, not along the entire stretch of the road.

Sight Distance

6. Superelevation

Superelevation is the practice of raising the outer edge of a roadway relative to the inner edge along horizontal curves. It helps counteract centrifugal force exerted by moving vehicles, thus enhancing safety and comfort.

Super-elevation

Superelevation Formula:

$$e + f = \frac{v^2}{gR}$$

where,

• $e$ = Superelevation

• $\mathrm{f }$= Lateral friction factor

• $v$ = Design speed in m/sec

• $g$ = Acceleration due to gravity

• $R$ = Radius of the horizontal curve in meters

IRC classification of the Roads/highways in India

Hello,
How you doing?


IRC(Indian Roads Congress) has classified the roads in the India in the following 5 categories:
(a) National Highways
(b) State Highways
(c) Major District Roads
(d) Other District Roads
(e) Village Roads

• National Highways(NH):  National highways are the major arterial roads spanning in the length and breadth of the country and connects the Capital to the various state capitals of the country or with the neighboring countries. 

They also connect the famous tourism places of the country. National highways are numbered and written as NH-1, NH-2 etc. They have the highest design specifications.

• 

 Example : NH -1 Delhi-Ambala-Amritsar, NH-21 Chandigarh- Mandi- Manali.

• State Highways(SH): State highways are the roads which connect the state capital to other states and to the district headquarters in the state.  They have design specifications similar to those of the National Highways because they carry enough traffic.

• Major District Roads(MDR): These roads connect the district headquarters to the main town centers in the district, and to the headquarters of the other districts also. They also connect these major town centers to the other state highways of importance. They have lower design specifications as compared to the NH and SH.

• Other district roads(ODR): These roads connect the rural areas town centers to the major district roads of higher importance.They provide the facilities for the transportation of the raw materials or the goods mainly of agricultural products from the rural towns to the higher markets and vice-versa.

• Village Roads(VR): These roads connect the rural villages with one another and to the nearest higher level road or to the nearest town center. They have lower design specifications and many of them are not even metaled.

Thanks for visit!

Functions of IRC, CRRI, and Roads wing of Surface Transportation

Hello there,

Appointment of the Jayakar Committee:

In 1927 central Govt. appointed an Indian Road development committee under the chairmanship of M.R. Jayakar  to report on the existing  road conditions, and suggestion for their future developments. 
The Jayakar committee submitted its report on 1928 with the recommendations that since the provincial governments and the local bodies are not able to look after all the roads; the road development in the country should be taken up by the Central Government.

Indian Roads Congress (I.R.C.):

The Indian Roads Congress was established by the Central Government in 1934 as per the recommendations of the Jayakar Committee. The I.R.C.  was constituted to provide a forum for the regular pooling the technical ideas,  experiences and  knowhow for the panning of the development of the roads throughout the country.  I.R.C.  provides the recommended specifications regarding the design and  construction of the roads in the country.  

IRC has collaborated with the road wing of the ministry of the surface transportation of Govt. of India. It publishes journals, standard specifications and guidelines on various aspects of highway engineering.

Functions of Indian Roads Congress (IRC):

IRC a body of professional highway engineers provides the following services:

(i) It provides a forum for expression of collective opinion of its members for all matters affecting the construction and maintenance of roads in India.

(ii) It promotes the use of the standard specifications and practices.

(iii)  It provided with the suggestions for the better methods of planning, designing, construction, administration and maintenance of roads.

(iv)              It conducts periodical meetings to discuss technical problems regarding roads.

(v)  It makes the laws for the development, improvement and protection of the roads.

(vi) It furnishes and maintains libraries and museums for encouraging the science of road making.

Functions of Central Road Research Institute (CRRI):

CRRI was started by the Central Government in 1950, for the research work in the highway engineering. CRRI is a series of laboratories under the council of scientific and industrial research in India. It offers the following services:

(1)    Carries basic and applied research for the design, construction and maintenance of the highways.

(2)    Carries research on traffic safety and transport economics.

(3)    Carries research on economical utilization of locally available materials for construction and maintenance of roads.

(4)    Research for the development of the new machinery, tools equipment and instruments for highway engineering.

(5)    To provide technical advice and consultancy services to various organizations.

(6)    To provide library and documentation services.

 Roads wing of ministry of surface transport:

The roads wing of the ministry of Surface Transport handles the road matters of the Central Govt. It is headed by a Director General.  
The Director General is assisted by two additional Director Generals(one for roads and one for bridges), a numbers of Chief Engineers, Superintending Engineers, Executive Engineers and Asst.
 Executive Engineers. The roads wing has a chief Engineer for the North-East region posted at Guwahati and a Liaison-cum-Inspectorate organization consisting of S.E’s and E.E’s in the various states. The functions of the roads wing of Surface Transport are:

(a)    To control funds approved by Central Government for the development of National Highways.

(b)   To control the central road fund.

(c)    To prepare plans for development and maintenance of National Highways in consultation with state PWD’s.

(d)   To oversee technically the quality of works executed by the agencies.

(e)   To administer matters regarding road research.

(f)     To examine technically the projects of roads and bridges prepared by the PWD’s.

(g)    To administer the central road program other than National Highways in the Union Territories. 

Thanks!

Highway Maintenance -Overlay Design

Overlay can be of many types:

(1) flexible overlay over a exiting flexible pavement

(2) flexible overlay over a rigid pavement.

(3) Rigid overlay  over a flexible pavement.

(4) Rigid overlay over a rigid pavement.

(1) Flexible overlay over flexible pavement by convention method of design:

h0 = hd - he

ho= thickness of the flexible overlay over flexible pavement .

hd= Design thickness of the flexible pavement

he= thickness of the existing pavement.

Analysis of Data:

Standard deviation of deflection:

Characteristic Deflection :

Overlay Thickness Design: 

ho= R/0.343 log10(Dc/Da)    ....Ruiz's equation.

ho= Thickness of bituminous overlay in cm.

R= Deflection reduction factor depending on the overlay material

As per IRC: 

ho=550log10(Dc/Da)

ho= Thickness of granular or WBM overlay in mm.

D = D(mean) +6, after applying the correction for the pavement temperature and sub grade moisture.

Da= 1.00, 1.25 & 1.50mm if the projected design traffic A is 1500 to 4500, 450 to 1500 & 150 to 450 respectively.

Rigid Overlay over Rigid Pavement:

Flexible overlay over Rigid Pavement:

hf =2.5(Fhd - he)

where, hf= Flexible overlay thickness

            he= Existing rigid pavement thickness

            hd= Design thickness of rigid pavement

     f= Factor which depend upon modulus of existing pavement.

hb= 1.66(Fhd - he)

where, hb= thickness of the bituminous overlay

Intelligent Transportation System(ITS)

Intelligent Transportation Engineering(ITS) is a system which uses the new innovations and technology to control and regulate the traffic. This system is also used to provide the users the required information.
The new technologies like, Automatic Traffic signals, CCTV, wireless communication devices in the hands of the traffic police, digital methods to calculate the traffic  volume etc. are the technologies which come under ITS.
Transportation users are kept informed of the various transportation services as per their requirements. Suppose you have reserved your seat in a bus, and you are waiting at the bus station for the bus. If due to some reason the bus is late, you will get the information about the bus being late so you can plan your time accordingly. All the updated information about the arriving and departures of the buses can be displayed with the electronic devices so one is always informed about all the schedule.
The traffic volume can be calculated using the GPS techniques, or some other sensing technique in which each vehicle is sensed with an unique identification number.  The floating car method is best method to calculate the amount of traffic.
Traffic control is now much easier, because their are various new useful technologies available in this sector. Their are speed sensors, which can detect if you are over speeding on the highways. In some countries they have developed a technique to avoid the collision. Their is this indicator, which will warn you if their is any other vehicle coming at speed from the another side. Their are dynamic speed limit indicators. 

Tunneling (Transportation Engineering)

Hi there,

 A tunnel is needed when an obstacle in the form of a hill or rising ground is met within the alignment of a highway or railway track. The first tunnel , about 4000 years ago of a cross section of 3.6 m * 4.5 m; 910 meter long, was built in Babylon connecting two buildings.

In Europe the first tunnel was built by Roman Emperor Claudius in 54 AD for carrying spring water through Apennines.  The cross of the tunnel was 3.0 m * 1.8 m and its length was 5.8 Km. It was completed in 12 years by 30, 000 laborers.

This article covers the following aspects of Engineering related with the Tunneling:

1. Sections of tunnels: advantages, limitations and suitability of each section
2. Shaft, pilot tunnel.
3. Driving tunnel in rocks, sequence of construction operations
4. Full face method, heading and bench method, drift method
5. Driving tunnels in soft ground, sequence of construction operations, needle beam method
6. Shield tunneling, compressed air tunneling.

• Sections of tunnels, suitability of each section:

In general you will find the four types of tunnel sections which are famous in tunneling:

1. Circular shaped tunnels
2. Elliptical
3. Horse-Shoe shape tunnels
4. Vertical walls with arched roof(D-Shaped tunnels).

The shape of the cross section of a cement concrete lined tunnel will depend on the pressure of the ground which the lining must be able to resist and the purpose for which the tunnel is to be constructed.

If the ground is solid rock, then any shape may be adopted but for soft ground such as soft clay or sand, the pressure from the sides as well from the top is to be resisted. In such difficult situations, circular cross section is best suited if it is able to serve the purpose of the tunnel.

A circular tunnel, in general is not suitable for the highways because highways need a flat surfaces. Circular sections are more suitable for aqua-ducts.

D-shaped tunnels have a horizontal base( flat invert), two vertical sides and an arched roof. Such tunnels are best suited as the vehicular tunnels.

 The semicircular top acts as an arch, and thus takes and shifts the top soil load to the vertical sides and thus to the bed. If the ground bed is broken, subjected to the horizontal pressure, vertical wall sections of a vehicular tunnel may be replaced with a horse shoe section as it can resist the external pressure better.

Circular and elliptical tunnels are popular for water(irrigation) and sewage conduits while the horse shoe and vertical wall sections (D-Shaped) sections are popular for vehicular tunnels depending upon the condition and type of ground.

• Shaft, Pilot Tunnel:

Shafts are the vertical tunnels, generally circular in section. In case of the hydro projects you have to construct the surge shafts to prevent the water hemorrhage. In the highway projects surge shafts are constructed from the top to reach down to the main tunnel and provides the access path to the main tunnels.

A numbers of shafts may be constructed at places more than one in a long tunnel project, and work may be started from those numbers of places. Diameter of a shaft depends upon the purpose of the shaft, if a TBM is to be lowered to the main tunnel than it is necessary to make the shaft of the required size.

Similar to a shaft Pilot tunnels serves as the access tunnels to the main tunnels. The cross section of a pilot tunnel is usually 240 cm or a little bigger and are driven parallel to the main tunnel. The pilot tunnel is first driven to the full length of the tunnel and is connected to the center line of the main tunnel at many points. From these points, the work of the main tunnel may be started and also they make is easy to take out the muck.  Uses of the pilot tunnels may be summarized in the following points:

1. It helps in providing proper ventilation to the main tunnel.
2. It helps in removing the muck from the main tunnel quickly.
3. It helps in providing proper lighting in the main tunnel.

Pilot tunnels also offers a path to reach to the main tunnel so that you can access it to go for the further construction. Pilot tunnels are constructed generally parallel to the main tunnel, and when in connects to the main tunnel path, you get two faces/two directions to excavate your main tunnel.

• Driving Tunnel in rocks, sequence of construction operations:

Actual sequence of the tunneling operations, will depend upon the site conditions, size of the tunnel  and method of construction. However, the general sequence of the operations carried out during construction of a tunnel is as given below:

1. Setting up and drilling
2. Loading holes with explosives and firing them.
3. Ventilation and removing the dust after the explosion.
4. Loading and hauling muck.
5. Removing the ground water if necessity arises.
6. Erecting supports for sides and roofs in necessity arises.
7. Placing reinforcement.
8.  Placing concrete lining.

There are several methods of tunneling, the method to be selected for a particular site will depend upon the size of the bore, the equipment available, the condition of the formation and the extent to which the timbering is required. Tunneling may be grouped into two groups:

1. Tunneling in hard rocks
2. Tunneling in soft rocks.

Tunneling in hard rocks is carried by one the following methods:

1. Full face method
2. Heading and benching method
3. Drift Method
4. Pilot tunnel method
5. Perimeter method

Here we will discuss the first three methods in details.

• Full Face Method

This method of tunneling is adopted when the length of the tunnel is more than 3 meters. Large sized tunnels in rocks are always driven by this method. With the development of drill carriage this method is becoming more and more popular. In this method vertical columns are fixed to the face of the tunnel to which a large number of drills may be mounted or fixed at any suitable height as shown in the figure below. A series of drill holes are drilled at about 120 cm center to center in any number of desired rows, preferably in two rows. The size of the holes may vary from 10 to 40 mm. These holes are then charged with explosives and ignited. The muck is removed before the next operation of drilling holes.

• Heading and Benching Method

Tunnel cross section is divided into two parts, the top portion of the tunnel is known as the heading and the bottom portion as bench. Usually this method is adopted for railway tunnels. In this method of tunneling, top portion or heading will be about 3.70 to 9.6 m ahead of the bottom portion as shown in the figure below. In hard rock which may permit the roof to withstand without supports, the top heading  generally is advanced by one round of bottom portion. If the rock is broken then heading may be driven well ahead of the bottom portion and after giving proper support to the roof, the bottom portion is completed. In hard rock the heading is bored first and the holes are driven for the bench portion at the same time as the removal of the muck. This required less explosive than the full face method, but due to the development of the drill carriage or jumbo, the use of this method is decreasing.

Heading and Benching Method (Tunneling)

• Drift Method:

Drift is a small tunnel, usually its size is 3m*3m. In driving a large tunnel it has been found advantageous to drive a drift first through the full length or in a portion of the length of the tunnel prior to the excavating the full bore.

Drift Method (tunneling)

The drift may be provided at the center, sides, bottom or top as desired. In this method after driving the drift, the drill holes are drilled all round the drift in the entire cross section of the tunnel, filled with explosives and ignited. The rock shatters, the muck removed and the tunnel expanded to the full cross section.

Driving tunnels in soft ground

 While tunneling in soft grounds, explosives are not used and tunneling is done with the hand tools such as pick-axes, shovels etc. During excavation operation supports for soil are required immediately depending upon the type of soil. In the old days, timber was the only material used for supporting soft ground till the introduction of the steel liner plates few years ago. As heavy supporting system is needed to support the roof and sides, there is more obstruction in the movement inside the tunnel, which reduces the progress of the work. Care should taken to ensure that all struts should be sufficiently strong to bear the pressure coming on them. The method to be adopted in the soft ground tunneling depends upon the type of ground.

• Needle beam method, sequence of construction operations 

This method is useful for tunneling in the soft ground whose roof soil can stand without support for few minutes. In this method 5 to 6 meters long R.S. joist or timber beams are required in addition to other timber boards and struts. This method requires large number of jacks which cause obstruction in the efficient working of the laborers. For tunneling in soft ground it is more economical than other methods.

• Sequence of Working: 

1. First of all a small drift of size of about 1*1 m is prepared on the working face of the tunnel.
2. The needle beam consisting of two I girders, bolted together with a wooden block at the center, is inserted in the drift and its roof is supported on lagging carried on the wooden segment as shown in the figure below. These segments are supported by jacks resting on the needle beam.

   

   Needle beam method- 1

3. As shown in the figure below, the needle beam is placed horizontally, whose front end rests on the drift itself and the rear end is supported on the vertical stout post, resting on the lining of the tunnel.

   

   Needle beam -2

4. The jack is placed on the top of the beam(Needle Beam) to support the roof with lagging and then drift is widened side ways and the whole section is excavated. After excavating lining may be provided. 

• Compressed Air Tunneling Method:

This method is considered as most modern method of tunneling in soft grounds having water bearing stratum. A compressed air is forced into the enclosed space to prevent the collapse of the roof and sides of the tunnel. 

Usually air is used in conjunction with a shield and air-tight locks. However, numerous small tunnels have been driven using only linear plates or wood cants only. This method can be safely adopted if the air pressure is approximately 1 kg/cm^2. If the pressure is more than 1 kg/cm^2, the working hours should be reduced considerably which will increase the cost of tunneling.

Application of the air pressure to the tunneling is not so simple due to the following reasons:

1. The earth pressure varies from the top of the tunnel to the bottom of the tunnel.
2. As the pressure in the floor of the tunnel depends upon the nature of the strata, it is difficult to ascertain it theoretically.
3. The value of pressure varies with the moisture content in different strata, which is difficult to ascertain. 
4. The compressed air will escape through the pores of the soil, hence air pressure will diminish continuously. Thus the value of air pressure will have to vary from time to time to get a balanced value and the determination of this value depends more on experience than theoretical considerations. 

This method is ideally suitable for clay formations which do not contain large number of pores and the pressure does not vary much from top of the tunnel to its bottom. 

Thanks for your kind visit!

Highway Geometrics- Short introduction

Hi,
You must know the various highway cross section elements if you are a highway engineer. You might have the introduction with the cross section elements like friction, camber, formation width, road width, super elevation and sight distance etc. To design a safe and economic road you must consider all these elements.
For safe and efficient running of the traffic it must have the required formation width. For the durability of the roads, it must have the required camber. Super elevation is required at the horizontal curves to keep the fast moving vehicles on the track. Sight distance is again very important in terms of safety and therefore for effective traffic movement. You must consider the Codal specifications to look for the standard values. In India Indian Roads Congress is an active organization which provides the specifications for design. In USA it is AASTHO.
If you are a highway engineer, then remember that you have the responsibility of the safety of the vehicles and the lives in terms of the road serviceability. Do your best and keep rest up to God.
If you have any suggestions to improve the article please leave a comment.
Thank you for reading.