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Solution to Previous Year Exam Questions for Highway and Traffic Engineering - HTE of DSATM by Saif Adnan

  • Highway and Traffic Engineering - HTE
  • 2016
  • PYQ Solution
  • Visvesvaraya Technological University Regional Center - VTU
  • Civil Engineering
  • B.Tech
  • 221 Offline Downloads
  • Uploaded 1 year ago
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HIGHWAY GEOMETRIC DESIGN 10CV755 ÿ Design Hourly Volume and Capacity: The general unit for measuring traffic on highway is the Annual Average Daily Traffic volume, abbreviated as AADT. The traffic flow (or) volume keeps fluctuating with time, from a low value during off peak hours to the highest value during the peak hour. It will be uneconomical to design the roadway facilities for the peak traffic flow. Therefore a reasonable value of traffic volume is decided for the design and this is called as Design Hourly Volume (DHV) which is determined from extensive traffic volume studies. The ratio of volume to capacity affects the level of service of the road. The geometric design is thus based on this design volume, capacity etc. ÿ Environmental and other factors: The environmental factors like air pollution, noise pollution, landscaping, aesthetics and other global conditions should be given due considerations in the geometric design of roads. 3. Enumerate the concept of PCU in geometric design of highways. List out the factors governing PCU. Give some typical values as recommended by IRC.( Dec2014/Jan2015, June/July 2015, Dec 2013/Jan 2014, Jan 2013) Ans: Passenger Car Unit (PCU): Different classes of vehicles such as cars, vans, buses, trucks, auto rickshaw, motor cycles, pedal cycles etc. are found to use the common roadway facilities without segregation. The flow of traffic with unrestricted mixing of different vehicle classes forms the ‘Mixed Traffic Flow’. In a mixed traffic condition, the traffic flow characteristics are very much complex when compared to homogeneous traffic consisting of passenger cars only. It is very difficult to estimate the traffic volume and capacity of roadway facilities under mixed traffic flow. Hence the different vehicle classes are converted to one common standard vehicle unit. It is common practice to consider the passenger car as the standard vehicle unit to convert the other vehicle classes and this unit is called Passenger Car Unit (or) PCU. Thus in a mixed traffic flow, traffic volume and capacity are generally expressed as pcu / hr (or) pcu / lane/ hr and traffic density as pcu / km length of lane. Dept. Of Civil Engg, SJBIT Page 2

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HIGHWAY GEOMETRIC DESIGN 10CV755 Factors affecting PCU Values: ÿ Vehicles characteristics such as dimensions, power, speed, acceleration and braking characteristics. ÿ Transverse and longitudinal gaps (or) clearances between moving vehicles which depends upon speed, driver characteristics. ÿ Traffic stream characteristics such as composition of different vehicle classes, mean speed and speed distribution of mixed traffic stream, volume to capacity ratio etc. ÿ Roadway characteristics such as road geometrics includes gradient, curve etc., rural or urban road, presence of intersections and the types of intersections. ÿ Regulation and control of traffic such as speed limit, one-way traffic, presence of different traffic control devices etc. ÿ Environmental and climatic conditions PCU values suggested by IRC: 4. Explain the geometric elements to be considered for the design of highway(June/July2015) (Or) Dept. Of Civil Engg, SJBIT Page 3

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HIGHWAY GEOMETRIC DESIGN 10CV755 5. Explain the objects of highway geometric design. List the various geometric elements to be considered in the highway design.( June/July 2015, Dec 2014/Jan 2015) Ans:The geometric design of highways deals with the dimensions and layout of visible features of the highway. The emphasis of the geometric design is to address the requirement of the driver and the vehicle such as safety, comfort, efficiency, etc. The features normally considered are the cross section elements, sight distance consideration, horizontal curvature, gradients, and intersection. The design of these features is to a great extend influenced by driver behavior and psychology, vehicle characteristics, track characteristics such as speed and volume. The objective of geometric design is to provide maximum efficiency, in traffic operations with maximum safety at reasonable cost. The emphasis of the geometric design is to address the requirement of the driver and the vehicle such as safety, comfort, efficiency, etc. Geometric design of highways deals with the following elements: ÿ Cross-section elements ÿ Sight distance considerations ÿ Horizontal alignment details ÿ Vertical alignment details ÿ Intersection elements 6. Explain significance of design speed and design vehicle in the geometries(June/July2013,Dec 2015/Jan 2016) Ans:Design speed: Design speed is the single most important factor that affects the geometric design. It directly affects the sight distance, horizontal curve, and the length of vertical curves. Since the speed of vehicles vary with driver, terrain etc., a design speed is adopted for all the geometric design. Design speed is defined as the highest continuous speed at which individual vehicles can travel with safety on the highway when weather conditions are conducive. Design speed is different from the legal speed limit which is the speed limit imposed to curb a common tendency of drivers to travel beyond an accepted safe speed. Design speed is also different from the desired speed which is the Dept. Of Civil Engg, SJBIT Page 4

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HIGHWAY GEOMETRIC DESIGN 10CV755 maximum speed at which a driver would travel when unconstrained by either track or local geometry. A “Design Vehicle” is a selected motor vehicle, the weight, dimensions and operating characteristics of which are used to establish highway design controls to accommodate vehicles of a designated type. The dimensions and operating characteristics of a vehicle profoundly influence the geometric design aspects such as radii, width of pavements, clearances, parking geometries etc. The weight of axles and the weight of the vehicles affect the structural design of the pavement and structures, as also the operating characteristics of vehicles on grades. Because of its crucial importance, the standardization of the dimensions and weights of design vehicles is the first step in formulating geometric design standards. This has been done in most countries. In India, the current standard of the Indian Roads Congress is generally followed . The AASHTO standards represent American practice. In U.K., the Ministry of Transport Regulations governs the features of the design vehicle. Types of design vehicles: The AASHTO Standard on Urban Streets (Ref. 4) classifies the following broad types of design vehicles: 1. Passenger Car Provisional P 2. Single Unit Truck SU 3. Single Unit Bus BUS 4. Semitrailer combination, intermediate WB—40 5. Semitrailer combination, large WE—50 6. Semitrailer full trailer combination WE—60 The IRC Standard contains only commercial vehicles of the following types: 1. Single unit truck. 2. Semi-trailer. 3. Truck-trailer combination. 7. Explain the important functional aspects of geometric design( Dec2013/Jan 2014) Ans: The functional aspects of geometric design are as follows Dept. Of Civil Engg, SJBIT Page 5

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