Super-elevation at horizontal curves

Hi,

Super-elevation: It is the inward transverse slope provided throughout the length of the horizontal curves to counteract the centrifugal force and therefore to check the tendency of the vehicle to over turn or skid.

Outer edge of the pavement is raised with respect to the inner edge of the pavement, the ratio of the height raised to the width of the pavement is called super-elevation.

Superelevation on the horizontal curves

e = E/B = tan(angle w.r.t. horizontal)

Or E = e.B

e+f = v^2/ g.R
Here, e = rate of super-elevation
          f= design value of the lateral friction co-efficient = 0.15
        v = speed of vehicle in m/sec.
        R= Radius of the horizontal curve, m
  If velocity is in Kmph, then
  e+f = V^2/(127.R)

Methods of Providing Super-elevation:

Superelevation is provided at a gradual rate along the length of the transition curve. It  is done by changing crowned camber  a single cross slope before the start of the circular curve.  Full superelevation is attained at the end of transition curve or at the start of the circular curve.

Attainment of the Superelevation may be completed in following steps:

(i) Elimination of the crown of the cambered section.

(ii) Rotation of the pavement to attain a full super-elevation.

Second step can be completed in three ways,  (a) by rotating the pavement with respect to inner edge,  (b) by rotating the pavement with respect to the center of the pavement or  (c) by rotating the pavement with respect to the outer edge of the pavement.

Superelevation is introduced by rise in the outer edge of the pavement at a rate not exceeding 1 in 150 in plain and rolling terrain and 1 in 60 on mountainous and steep terrain as per the recommendations of the IRC(Indian Roads Congress).

Designing Superelevation:

The design procedure for providing the superelevation follows the following Four steps:

(1) Friction is neglected and super-elevation is designed for 75% of the design speed value,

     e = (0.75. v)^2/ (gR)   where v is in m/sec

 or e = (0.75. V)^2/ (127R)   where v is in Kmph/sec

(2) If e < 0.07 then value so obtained is provided

If e>0.07, then provide the maximum super-elevation equal to 0.07 and proceed with steps 3 and 4.

(3) Check the co-efficient of friction developed for the maximum value of e equal to 0.07 for the full design speed v.
   f= v^2/(g.R) - 0.07
if  f< 0.15, then e = 0.07 is safe for the design speed. If not, calculate the restricted speed as follows

(4) 0.07 + 0.15 = Va^2/ (g.R)
         Where, Va = allowable safe speed.

Thanks for visit!

Widening of Pavement on Horizontal Curve

Hi, 

If you have observed the pavement width on the horizontal curves, you will find that to be somewhat larger than the width on the straight roads. The pavement is extra widened on the horizontal curves due to the following reasons:

1. The wheel base of the vehicles is rigid and therefore while taking the turn, only front wheel are able to change direction. Path traveled by the front will be different and will be at certain distance outwards from the path traced by the inner wheel. This can be understood with the help of the diagram and image shown below.

   

   Extra widening on horizontal curves

2. There is a tendency of the driver to take the outer path at the curves to have more sight distance visible ahead.
3. While overtaking operations on horizontal curves driver will need more spacing from the other vehicles to feel safer.

Widening of the Pavement on the Horizontal Curves:

Horizontal curve on a hilly road (Gocind Sagar view point-Himachal Pradesh)

Widening of the pavement on the horizontal curves is governed by the following factors:

(a) Length of the wheel base

(b) Radius of the curve negotiated, R

(c) Psychological factor which depends upon the velocity of the vehicle and the Radius of the curve.

 In general extra width is provided on the horizontal curves when the radius is less than 300 m.

Now, 

Extra widening = mechanical Widening + Psychological Widening

IRC recmmended values for the Extra widening of pavement on Horizontal curves

           We = Wm + Wps

           We =  nl^2/ 2R + V/ [9.5R^(1/2)]

Here, n = number of traffic lanes

           l = Length of the wheel base

           V= Design speed in kmph

            R = Radius of the horizontal curve in m

The figure given above shows the IRC recommended values of the extra width for the curves of different radius.

Thanks for your kind visit!

Highway Curves

Hi,
Here are the images which explains the Highway curves, be it horizontal or vertical curves. Horizontal curves are simple circular curves, compound curves, reverse curves etc.
There are transition curves, and at end vertical curves are explained.

Thanks for the kind visit!

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

---

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.

---

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