*DOWNLOAD AND PLAY IN MICROSOFT POWERPOINT* 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 (3RD 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
𝑸𝒘 =
280𝑤 1 +
𝑒
𝑤
[1 −
𝑝
3
]
[1 +
𝑤
𝑙
]
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.
 Four types of movements at a weaving section, and are the
non-weaving traffic and are the weaving traffic.
p =
𝒃+𝒄
𝒂+𝒃+𝒄+𝒅

8. Design consideration 8
 Length of Intersecting straights with minimum site dist
ances 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 f
or speeds 50 km/h., 65 km/h., 80 km/h, 100 km/h. resp
ectively. 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 foun
tains, painted with colours in contrast with the road pa
vement.
{1-(a/b)2} R4-{b2-5a2/4} R2 –(a2b2/2) = 0

9. Operational Requirements
 Provide adequate sight distance – for approac
h and departure maneuvers
 Minimize turning and through conflicts
 Provide natural paths for permitted movemen
ts
 Avoid geometry (sharp curves/steep grades)
that complicates the driving task and adverse
ly impacts acceleration or deceleration
9

10. Intersection Sight Distan
ce – ISD
 Allow drivers to have an unobstructed view of i
ntersection
 Required ISD is the length of cross road that
must be visible such that the driver of a turnin
g/crossing vehicle can decide to and complete t
he maneuver without conflict with vehicles appr
oaching the intersection on the cross road.
10

11. Adequate ISD
 Sight Triangle – area free of obstructions nece
ssary to complete maneuver and avoid collision
– needed for approach and departure (from sto
p 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
 Area free of obstructions necessary to comp
lete maneuver and avoid collision – needed fo
r approach and departure (from stop sign for
example)
 Consider horizontal as well as vertical, objec
t below driver eye height may not be an obst
ruction
 AASHTO assumes 3.5’ above roadway
12

13. 13

14. 14
Sight Distance Obstructions
Hidden Vehicle

15. ISD Cases
 No control: vehicles adjust speed
 Stop control: where traffic on minor roadwa
y must stop prior to entering major roadway
 Yield control: vehicles on minor roadway mu
st yield to major roadway traffic
 Signal control: where vehicles on all approac
hes 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 dis
tance provided?

17. 17
Large T
ree
a = 47’
b = 72’
Example
50 mph
25 mph
25 mph > 15 mph, stopping sight
distance is not sufficient for
25 mph
db
da
bd
d
ad
a
a
b


da = 220 feet
db = 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 Uncontrolle
d Intersection 19
Observer
Assistant
Decision
Point
Obstruction
X
Y

20. 20
Observer
Assistant
Movement of Assistant

21. Measuring at a Stop-controlled
Intersection
21
Observer
Assistant
Stop Bar
10 ft
SightLine

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

23. THANK YOU
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