Transportation Engineering (General Engineering) (SSC JE)

According to IRC, the maximum super elevation is given by

• Transition curve is curve in plan, which is provided to change the horizontal alignment from straight to circular curve gradually means the radius of transition curve varies between infinity to R or R to infinity.
• IRC recommends spiral or clothoid as the load transition curve.

As per IRC, the centrifugal force corresponding to 75% of the design speed is counteracted by providing the super elevation or horizontal curve, so speed gets reduced by 100 – 75 = 25%.

30th highest hourly volume–It is that hourly volume which will be exceeded only 29 times in a year and all other hourly volume will be lesser than this. It is used to design the highway elements and also called as design hourly volume.

Annual Average Daily Traffic (AADT)–It is the average volume of traffic at a particular location over a full 365 days and it is given as

Spot speed–It is the instantaneous speed of a vehicle at any specified point. The spot speeds are affected by physical features of road such as pavement width, curve, sight distance, gradient pavement unevenness and road side development.
There are number of methods of measure spot speed–
(a) Enoscope method or mirror box method
(b) Photographic method
(c) Electronic method
(d) Radar speed meter method.
• Most simplest method of finding spot speed is by wing enoscope.

The maximum width of a vehicle as recommended by IRC is 2.44 m.
• Maximum height–If affects the clearance of the overhead structure and visibility of driver.
(a) Single decked vehicle = 3.80 m
(b) Double decked vehicle = 4.75 m

Maximum length–It affects the capacity, OSD and movability of vehicle (a) Single unit truck with two or more axles = 11.0 m
(b) Single unit bus with two or more axles = 12.0 m
(c) Semi trailer tractor combinations = 16.0 m
(d) Tractor and trailor combinations = 18.0 m

Origin and destination studies–This studies generally carried out to
(i) Plan the road network and other facilities for vehicular traffics.
(ii) Plan the schedule of different modes of transportation for the trip demand.
(iii) To judge the adequacy of existing router and use in planning new network of roads.
(iv) To locate expressway or major routes along the desires lines.
(v) To establish preferential routes for various categories to vehicle including by pass.

Practical capacity–It is the maximum number of vehicle that can pass a given point on a lane or roadway during one hour, without traffic density being so great as to cause unreasonable delay, hazard or restriction to the drivers freedom to manoeuvse under the prevailing roadway and traffic condition. This also known as design capacity.

Basic capacity–It is the maximum number of vehicles that can pass a given point on a lane or roadway during one hour under the most nearly ideal roadway and traffic condition which can possibly be at trained.

Abrasion test–Abrasion test carried out to test the hardness property of aggregate. It is the best test of aggregate which includes abrasion, attrition and impact.
Different type of abrasion tests are–
1. Los Angeles abrasion test
2. Dorry abrasion test
3. Dovel abrasion test
Note–
Abrasion - Rubbing between aggregate and steel ball
Attrition - Rubbing between aggregate and aggregate