## Posts

Showing posts from August, 2013

### Sight Distance - Stopping Sight Distance and Overtaking Sight Distance

Sight Distance: It is the length of the road ahead visible to a driver at any instance. IRC (Indian Roads congress) has standardized the definition by assuming the eye level of driver as 1.2 m above the road surface and height of obstruction 0.15 m from the road surface.
There are three main important sight distances, which are considered for the design of the roads:
(a) Stopping Sight Distance
(b) Overtaking Sight Distance
(c) Sight Distance at the Intersections

(a) Stopping Sight Distance: Stopping Sight Distance is the sight distance required for a driver to effectively apply the brakes and stop the vehicle without collision with the obstruction on the road.
Stopping Sight Distance = Lag Distance + Braking Distance = v.t + v^2/2gf   where, v is in m/sec

(b) Overtaking Sight Distance: Overtaking Sight Distance is the sight distance which is required by the vehicle running at the design speed to overtake a vehicle running in the same lane at relatively smaller speed.
OSD = d1+ d2+ d3…

### Length of Transition Curves

Length of Transition Curves: Transition curves are provided in between a straight road and the Curve of a design radius. So the radius of a transition curve varies from infinity to the design radius or vice verse.  The length of the transition curve must fulfill some requirements. It is designed to fulfill the following three conditions: (a) Rate of change of centri-fugal Acceleration(C):  C = (v^2/R)/t =  (v^2/R)/ (Ls/v) = v^3/( LsR)  m/sec^3
As per IRC recommendations, C= 80/(75+v)   m/sec^3
Here, C= allowable rate of change of centrifugal acceleration ( m/sec^3) Ls= Length of the transition curve.
(b) Rate of introduction of Designed super-elevation: If pavement is rotated about centre line,  then 1/N = (E/2)/Ls => Ls= EN/2 = e.B.N/2 = e.(W+We).N/2
If pavement is rotated about inner edge, then I/N = E/Ls => Ls= EN = e.B.N= e.(W+We).N  where, Ls= Length of transition curve               B= width of the pavement (c) By Empirical Formula given by IRC(Indian Roads congress):        …

### Super-elevation at horizontal curves

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.

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: Super-elevation 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 super-elevation is attained at the end of transition curve or at the start …

### 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:
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. There is a tendency of the driver to take the outer path at the curves to have more sight distance visible ahead.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:
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) Psych…

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

Hello,  Highway Geometric: This is the branch of the highway engineering which deals with the geometrical elements of the roads like, land of width, formation width, carriage way, side slopes, shoulders, kerbs, sigh distance, super elevation and highway curves.Land Width: It is total width of the land acquired by the Govt. along the road for the construction and maintenance of the roads. No other buildings by public can be constructed on the land width. Land width depends upon the following factors:
(a) It depends on the type of the road to be constructed, like NH require more width as compare to the lower level highways. (b) It depends on the anticipated future increase in the traffic on the route or the economic or industrial development of the areas which it aligns along its route. Carriage Way:   It is the width of the road which is used by the traffic for moving on it. It is generally central portion of the total land width and is paved and surfaced with the bituminous concrete for se…

### 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
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 dist…

### 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. Jayakarto report on the existingroad 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 andknowhow for the panning of the development of the roads throughout the country.I.R.C.provides the recommended specifications regarding the design andconstruction of the roads in the country.IRC has collaborated with the road wing of…

### 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 45…