Design of rotary

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It includes the design, sight distance, ISD, Intersections, etc.

1. DESIGN OF ROTARY Prepared By – SUVAM PATRA SUBHAJIT KUNDU SOUVIK MONDAL SOMESH DE KARMAKAR SAYAN ROY SATYAKI SEN Department of civil engineering (3 rd year) 1

2. Definition 2 Rotary intersections or round- abouts are special form of at-grade intersections laid out for the movement of traffic in one direction around a central traffic island. The vehicles entering the rotary are gently forced to move in a clockwise direction in orderly fashion.

3. Intersections 3 More complicated area for drivers Main function is to provide for change of direction Source of congestion in urban areas Concern for safety (fender benders in urban, fatals in rural )

4. Types of Intersections Grade separated with ramps (freeway interchange) Grade separated without ramps (over or underpass with no access) At-grade Conventional Roundabouts New concepts (e.g., “continuous flow”) 4

5. Design Objectives “ To reduce the severity of potential conflicts between motor vehicles, pedestrians, and facilities while facilitating the convenience, ease, and comfort of people traversing the intersection.” AASHTO Provide ease/control of access consistent with the function of intersecting roadways 5

6. Width of Rotary 6 IRC suggest that a two-lane of 7m width should be kept as 7m for urban roads and 6.5 for rural roads. Further for a three-lane road ofb10.5m is to be reduced to 7m and 7.5m respectively for urban and rural roads . The width of weaving section should be higher than the width at entry and exit. The weaving with is given as , W weaving= {(e1+e2)/2} +3.5 m where, e1 = width of carriageway at the entry e2 = width of carriageway at the exit

7. Capacity 7 Transportation road research lab (TRL) proposed the following empirical formula to find the capacity of the weaving section where is the average entry and exit width, is the weaving width, is the length of weaving, and is the proportion of weaving traffic to the non-weaving traffic. F our types of movements at a weaving section, and are the non-weaving traffic and are the weaving traffic . p =  

8. Design consideration 8 Length of Intersecting straights with minimum site distances recommended by I.R.C. are: 50 km/h. Minimum Sight distance 15 m along minor roads Weaving Distance = 110 m, 145 m, 180 m and 220 m for speeds 50 km/h., 65 km/h., 80 km/h, 100 km/h. respectively. Minimum Weaving length: 30 to 50 m All traffic islands are constructed 200 mm higher than road level. They are provided with lawn, statue or fountains, painted with colours in contrast with the road pavement . { 1-(a/b)2} R4-{b2-5a2/4} R2 –(a2b2/2) = 0

9. Operational Requirements Provide adequate sight distance – for approach and departure maneuvers Minimize turning and through conflicts Provide natural paths for permitted movements Avoid geometry (sharp curves/steep grades) that complicates the driving task and adversely impacts acceleration or deceleration 9

10. Intersection Sight Distance – ISD Allow drivers to have an unobstructed view of intersection Required ISD is the length of cross road that must be visible such that the driver of a turning/crossing vehicle can decide to and complete the maneuver without conflict with vehicles approaching the intersection on the cross road. 10

11. Adequate ISD Sight Triangle – area free of obstructions necessary to complete maneuver and avoid collision – needed for approach and departure (from stop sign for example) Allows driver to anticipate and avoid collisions Allows drivers of stopped vehicles enough view of the intersection to decide when to enter 11

12. Sight Triangle A rea free of obstructions necessary to complete maneuver and avoid collision – needed for approach and departure (from stop sign for example) Consider horizontal as well as vertical, object below driver eye height may not be an obstruction AASHTO assumes 3.5’ above roadway 12

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14. 14 Sight Distance Obstruction s Hidden Vehicle

15. ISD Cases No control: vehicles adjust speed Stop control: where traffic on minor roadway must stop prior to entering major roadway Yield control: vehicles on minor roadway must yield to major roadway traffic Signal control: where vehicles on all approaches are required to stop by either a stop sign or traffic signal All way stop Stopped major roadway left-turn vehicles – must yield to oncoming traffic 15

16. 16 Large Tree 47’ 72’ Example 50 mph 25 mph Is sufficient stopping sight distance provided?

17. 17 Large Tree a = 47’ b = 72’ Example 50 mph 25 mph 25 mph > 15 mph, stopping sight distance is not sufficient for 25 mph d b d a d a = 220 feet d b = 47’ (220’) = 69.9’ 220’ – 72’

18. Sighting Rod and Target Rod (AASHTO) For vertical sight distance with vertical curves Sighting rod- 3.5 feet tall Target rod- 4.25 feet tall (Top portion and bottom 2 feet are painted orange) 18 Sighting Rod Target Rod

19. Measuring at an Uncontrolled Intersection 19 Observer Assistant Decision Point Obstruction Sight Line X Y

20. 20 Observer Assistant Movement of Assistant

21. Measuring at a Stop-controlled Intersection 21

22. 22 Assistant with Target Rod (4.25 ft ) Observer with Sighting Rod (3.5 ft )

23. THANK YOU 23