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.