Wednesday, January 1, 2014

One liners - Transportation Engineering for GATE, PSUs - Part 6

Hello there,
How have you been? Here is another round of one liners for your preparation for the GATE and PSUs examinations.
  • A traffic rotary is justified where number of intersecting roads is between 4 to 7.
  • When a number of roads are meeting at a point and only one of the roads is important, then the suitable shape of rotary is tangent.
  • Maximum number of vehicles can be parked with 90 degree parking.
  • When the width of kerb parking space and width of street are limited, generally preferred parking system is parallel parking
  • As per IRC recommendations, the average level of illumination on important roads carrying fast traffic is 30 lux.
  • The most economical lighting layout which is suitable for narrow roads is single side lighting.
  • The direct interchange ramp involves diverging to the right side and merging from right.
  • In soils having same plasticity index, if liquid limit is increased, then compressibility and permeability increases but dry strength decreases.
  • Aim of the Impact test is to check the toughness of road aggregates.
  • Los Angleles testing machine is used to find the abrasion value.
  • In Dorry's abrasion test, Hardness = [20 - (loss in weight/3)].
  • In CBR test the value of CBR is calculated at 2.5 mm and 5 mm penetrations.
  • If impact value is between 20 to 30, aggregate is satisfactory for road surfacing.
  • The maximum allowable Los Angeles abrasion value for high quality surface course is 30%.
  • Percentage of free carbon in bitumen is less than that in tar.
  • The ductility value of bitumen for suitability in road construction should not be less than 50 cm.
  • The maximum limit of water absorption for aggregate suitable for road construction is 0.6%.
  • Penetration test is performed to find out the grade of the bitumen.
  • Bitumen of grade 60/70 means, its penetration value is 6 to 7 mm.
  • The recommended grade of tar for grouting purpose is RT-5.
  • Softening point of bitumen to be used for road construction at a place should be above the maximum temperature at that place.
  • For rapid curing cut-backs gasoline is used as oil.
  • As per IRC recommendations CBR method is preferred for design of flexible pavements.
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