One liners - Transportation Engineering for GATE, PSUs - Part 5

Hello there,
How have you been? Here is another round of one liners for your preparation for the GATE and PSUs examinations.

• The diagram which shows the approximate path of vehicles and pedestrian involved in accidents is known as collision diagram.
• With increase in the speed of the traffic stream, the minimum spacing of vehicles increases.
• Traffic volume is equal to  traffic density * traffic speed.
• Practical capacity is also known as design capacity.
• With increase in speed of the traffic stream, the maximum capacity of the lane first increases and then decreases after reaching a maximum value at optimum speed.
• Equivalent factor of passenger car unit(PCU) for a passenger car as per IRC is 1.0.
• Scientific planning of transportation system and mass transit facilities in cities should be based on origin and destination studies.
• The diagram which shows all important physical conditions of an accident location like roadway limits, bridges, trees and all details of roadway conditions is known as condition diagram.
• When the speed of traffic flow becomes zero, then traffic density attains a maximum value whereas traffic volume becomes zero.
• On a right angled road intersection with two way traffic, the total number of conflict points is 24.
• The background of informatory  sign board is yellow.
• Level crossing is indicated by a warning sign.
• "Dead Slow" is a regulatory sign.
• The most efficient traffic signal system is flexible progressive system.
• The provision of traffic signals at inter-sections reduces right angled collisions but may increase rear end collisions.
• Stop or red time of a signal is the sum of go and clearance for the cross flow.
• Clearance time is generally 3 to 5 seconds.
• The cycle length is normally 40 to 60 seconds for two phase signals.
• Centre line markings are used in roadways meant for two way traffic.
• The particular places where pedestrians are to cross the pavement are properly marked by the pavement marking known as crosswalk lines.
• The entrance and exit curves of a rotary have different radii and different widths of pavement.
• When two equally important roads cross roughly at right angles, the suitable shape of central island is circular.
• Beyond 5000 vehicles per hour the rotary may not function efficiently.

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One liners - Transportation Engineering for GATE, PSUs - Part 4

Hello There,
I am here to give you another round of one liners from Surveying, for your preparation for GATE and PSUs.

• For a constant value of co-efficient of lateral friction, the value of required super-elevation increases with, increase in speed and with decrease in radius of curve.
• To calculate minimum value of ruling radius of horizontal curves in plain, the design speed is given by 16 kmph.
• The attainment of super-elevation by rotation of pavement about the inner edge of the pavement avoids the drainage problem in the flat terrain.
• Psychological extra widening of pavement depends upon the speed of the vehicle.
• In case of hill roads the extra widening is generally provided on the inner side of the curve.
• The mechanical widening required for a n lanes road is given by   (nl^2)/2R where, l is the length of wheel base of vehicle in meters.
• As per the recommendation of IRC, spiral curve is used as the transition curve in the horizontal alignment of the highways.
• The lower among the values obtained on the basis of allowable rate of change of centrifugal acceleration and based on rate of change of super-elevation, is taken as the design length.
• The maximum design gradient for vertical profile of a road is ruling gradient.
• The camber of a road should be approximately equal to half the longitudinal gradient.
• A cubic parabola is preferred in a valley curve.
• The value of ruling gradient in plains as per the recommendation of IRC is 1 in 30.
• Highway facilities are designed for thirtieth highest hourly volume.
• Enoscope is used to find the spot speed.
• For highway geometric design purposes the speed used is 98th percentile.
• Traffic capacity should always be greater than the traffic volume.
• Length of a vehicle affects extra width of pavements and minimum turning radius.
• The maximum width of a vehicle as per the recommendation of IRC is 2.44 m.
• Desire lines are plotted in origin and destination studies.
• License plate method is preferred for collecting origin and destination data for a small area like a mass business centre or a large intersection.

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Reference: Civil Engineering Objectives by S P Gupta and S P Gupta.

One Liners/MCQs- Transportation Engineering.- part 3

Hello,

Here are few MCQs which might help you with Transportation Engineering.
For more you can write below in the comment box or join my Facebook Page.

1. The camber preferred in concrete roads is

(a) Parabolic Camber

(b) Straight Camber

(c) Combination of parabolic and straight camber

(d) Cubic

Ans: (b) Straight

2. The shoulders are preferred to be

(a) Paved

(b) Rough

(c) Smooth

Ans: (b)

3. To avoid overturning and lateral skidding, the centrifugal ratio and lateral friction must be 

(a) Equal to b/2h

(b) More than b/2h

(c) Less than b/2h

(d) 0

  where b is the wheel base and h is the height of the center of gravity.

Ans: (c)

4. When the longitudinal distance covered is more than the wheel circumferential distance, this phenomenon is called:

(a) Sliding

(b) Skidding

(c) Overturning

(d) Decelerating

Ans: (b)

5. Nagpur road plan was based on 

(a) Star/Radial Road Pattern

(b) Rectangular road pattern

(c) Star/Radial and rectangular road pattern

(d) Star and Grid Pattern

Ans: (d)

 please help to upgrade the article.

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Rings and Balls Apparatus (Softening point test of Bitumen)

Softening point of Bitumen: It is the minimum temperature at which bitumen get soft.
It is important to find the softening point of Bitumen because bitumen can be easily applied on the road surface when it is soft and we have to use the fuel and fire to soften the available bitumen. Softening point tells us about the amount of fuel/energy that will be needed to soft it before applying on the road surface. Softening point of bitumen must not be below the average day temperature and it should also not be very much higher, because that will require much energy and fuel to soft it before applying on the road.

• Aim: To find out the softening point of the given bitumen sample.
• Apparatus: 

1. Rings and Balls Apparatus
2. Heating arrangement
3. Thermometer.

Rings and Balls Apparatus

Ring and Balls apparatus contain metallic rings and steel balls and a base metallic plate, encased inside a jar. This whole arrangement is immersed in the water inside the jar, so as to gradually and uniformly raise the temperature by heating with the help of the heating arrangement.

• Theory: Theory of this test is that as the temperature rises, bitumen starts to soft, and attains certain fluidity sufficient enough for this to be applied on the road surface. The temperature plays an important role in the hardness or the softness of the bitumen so we have to find out the minimum temperature at which bitumen attains sufficient fluidity.

• Procedure: 

1. Fill the top surface of the metallic rings with the given bitumen, forming a sheet like surface.
2.  At lower temperature surface of the bitumen will be hard enough to support the steel balls on the top surface, so put the steel balls on it just above the rings. 
3. When the whole arrangement immersed in the water is heated at the specified standard rate, the bitumen will start to soft and the steel balls under their own weight, will start to sink on the bitumen surface. 
4. Steel balls will sink in a way that they will drag the bitumen along with them in the downward direction, bitumen still supporting them but elongating at the same time. 
5. At certain rise of temperature, steel balls will touch the surface of the base plates below and that temperature is noted.  Thermometer must be put in through the slot initially to take the readings.

Result: The reading on the thermometer gives the softening point of the bitumen.

Road Materials - Soil as Sub-grade

Hi,
Road Materials are the materials which are used for the construction of the roads, commonly used road materials are, soil, Aggregates and binders.
Soil is used for the construction of the bottom most layer of the pavement, i.e. sub-grade. Here is a short details of the sub-grade and its function.:

Soil as sub-grade material

• sub-grade is the layer of the pavement whose main function is to support the upper layers of the pavement and to provide the good drainage facility to the infiltrating rain water. It has to act as a single structure along with other layers of the pavement.
• Soil is compacted to its maximum dry density which can be achieved by using the optimum moisture content and the methods of compaction control. Strength has to be ensured which is required for the given design thickness of the pavement.
• Strength analysis and the thickness of pavement are inter linked because more thickness of the pavement is needed if the soil is weak but if the soil possess a good strength then less thickness is needed.

This is ensured by using the CBR(California Bearing Ratio) Test which is produced or was first used by the California State Highway Department. Using the CBR test and the empirical charts you can find out the thickness of the flexible pavement required above the sub-grade.

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P.S. for more about the functions of the various pavement layers please visit this article:  Functions of various pavement layers.

Westergaard's theory for rigid pavements

Hi, 

Rigid Pavements are constructed with some rigid materials like Cement Concrete(Plain, reinforced or prestressed).

Here the load is transferred  through the slab action not like in the flexible pavements. Westergaard's theory is considered good to design the rigid pavements.

He considered rigid pavement slab as a thin elastic plate resting on soil sub-grade, which is assumed to be a dense liquid. So, here the upward reaction is assumed to be proportional to the deflection, i.e. p = K.d, where K is a constant defined as modulus of subgrade reaction. Units of K are kg/cm^3.

• Westergaard's modulus of sub-grade reaction:

Modulus of sub-grade reaction is proportional to amount of deflection d. Displacement level is taken as 0.125 cm in calculating K i.e. d = 0.125 cm, so modulus of sub-grade reaction
K = p/d = p/0.125 kg/cm^2

• Radius of relative stiffness of slab to sub-grade:

Amount of deflection which will occur on the pavement surface depends on the stiffness of the slab and also on the stiffness of the sub-grade. Same amount of deflection will occur on the top surface of the sub-grade.

This means that the amount of deflection which is going to occur in the rigid pavement pavement layer depends both on relative stiffness of the pavement slab with respect to that of sub-grade.

Westergaard defined this by a term "Radius of relative stiffness" which, can be written numerically as below:
            l = [Eh^3/ (12K(1-U^2)]^(1/4)

Where,  l = radius of relative stiffness, cm
         E = Modulus of elasticity of cement concrete kg/cm^2
         U = Poisson's ratio for concrete = 0.15
         K = Modulus of Sub-grade reaction in kg/cm^2

Traffic Parameters:
(1) Design Wheel Load
(2) Traffic Intensity

• Critical Load Positions:

  

  Rigid Pavement - a 3D view

When the wheel load is applied on the pavement surface, flexural stresses are induced in the pavement. There are three critical positions which are to be checked for maximum stresses.

1. Interior loading
2. Edge Loading
3. Corner loading

Whenever loading is applied at the interior of the slab, remote than the edges and corner, this is called interior loading.

When loading is applied on the edges, remote than the corners is called edge loading.

When the loading is applied on the corner angle bisector and loading is touching the corner the edges.

• Equivalent Radius of Resisting section:

When the loading is at the interiors there is a particular area which will resist the bending moment. Westergaard assumed that the area will be circular in plan and its radius is called as Equivalent radius of Resisting section.

Numerically,

     b= (1.6.a^2 + h^2)^(1/2)  - 0.675.h

Here,

      b = equivalent radius of resisting section, cm when 'a' is less than 1.724.h

      a = radios of wheel load distribution, cm

      h = slab thickness, cm

When 'a' is greater than 1.724.h, b =a.

• In case of corner loading, maximum stresses are not produced at corner but they are produced at a certain distance X along the corner bisector. This is given by the relation:

     X = 2.58.(a.l)^1/2

 Here,    X = distance from apex of the slab corner to section of maximum stress along the corner bisector, cm.

   a= Radius of wheel load distribution, cm

    l = Radius of relative stiffness, cm.

Here is an image which shows you the formulas used to calculate the amount of stresses developed at the three critical positions due to the given wheel load P.

Rigid Pavement- Stresses at interior, edges and corners - Westergaard's theory

References:
 

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Part -2-GATE preparation - Transportation Engg. - One liners

5. What is the value of intermediate sight distance for a highway with a design speed of 65 kmph? Assuming the data for co-efficient of friction f = 0.36 and for reaction time t = 2.5 sec.
Ans: 182.8 m

6. The speed of overtaking and overtaken vehicles are 70 and 40 kmph respectively on a two way traffic road. If acceleration of overtaking vehicle is 0.99 respectively, then safe overtaking sight distance, assuming reaction time of 2 sec, will be  278 m.

7. What is the minimum length of overtaking zone for a design speed of 96 kmph assuming acceleration as 0.69 m/sec^2, reaction time as 2 sec and traffic as one way?   Ans: 1026 m  OSD = 3(d1+d2)

8. The radius of horizontal circular curve is 100 m. If design speed is 50 kmph and design co-efficient of lateral friction is 0.15, then super elevation required if full lateral friction is assumed to develop will be 0.047

9. What is the co-efficient of friction needed if no super elevation is provided for a horizontal circular curve of radius 190 m and design speed of 65 kmph?   Ans: 0.177

10. Ruling minimum radius of horizontal curve of a national highway in plain terrain for a ruling design speed of 100 kmph with e = 0.07 and f = 0.15, is close to  360 m.

11. Design rate of super-elevation for horizontal highway curve of radius 450 m for a mixed traffic condition, having a speed of 125 km/hour, is 0.07

Refer GK Publishers for elaborated answers.