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INTRODUCTION
GENERAL
Phenominal growth of motor vehicles in Indian cities has been
creating enormous stress particularly at intersections. Major road
junctions suffer from inadequate and inefficient traffic control system
which invariably results increased delay and road accidents. Due to
increase in delay and congestion at most of the intersections there hasbeen a great loss to the society in terms of time loss in waiting at the
intersections and the excess fuel consumed by motorized vehicles.
Therefore there is an alternative need to look for an efficient
alternative solution to the existing problem to ensure more efficient
and less expensive travel both for the present and future traffic.
A possible remedy is to separate the grades of the intersecting
roads in the form of grade separated intersections. In developing
countries grade separation is adopted successfully to control and
reduce traffic congestion and accidents at intersections.
Grade separation is essential for managing traffic at major
intersections. In big cities, this type of intersection causes least delay
and hazard to the crossing traffic and in general is much superior to at
grade intersections from the point of view of traffic safety and efficient
operation. It eliminates all crossing conflicts at the intersection. There
are two types of grade separated intersection with interchange and
without interchange. Interchange is a system where by facility is
provided for the movement of traffic between two or more roadways at
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different levels in the grade separated junction. A structure without an
interchange is an over bridge or underpass or grade separator whereby
traffic at different levels moves separately.
NEED FOR THE STUDY
Grade separation is the highest form of intersection treatment.
The code for grade separator design practiced in our country is for
homogeneous traffic system, but the traffic system prevailing in our
country is heterogeneous. Hence the code has to be evaluated
whether it suits for Indian traffic flow.
Certain geometric standards like acceleration and deceleration
lane, ramp, gradient, distance between two grade separators need to
be studied, analyzed and compared with standards.
Along a major corridor many intersections are present and grade
separator is constructed at a major intersection to avoid congestion.
The congestion avoided in the major intersection moves to the next
minor intersection present along the corridor. Hence grade separator
constructed at the major intersection may not serve its purpose. Hence
the form, shape of the grade separator and the topography and
geometry of the area should be analyzed before construction of grade
separator.
Grade separators have to be evaluated to check whether the
deceleration lane is within the standards and whether it is possible to
reach a safe speed before reaching an intersection, as otherwise it
may lead to accident. If the ramp gradient provided is more or the
acceleration lane is less then it may cause difficulty for vehicles to
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climb up. The safe distance between two grade separators has to be
evaluated or otherwise it may lead to ride with roller coaster effect.
OBJECTIVES
The objectives of the study are the following
To study the traffic characteristics, traffic movement, accident
history
To compute the benefits of reduction in delay and accident and
To evaluate performance of existing grade separation facility
STUDY METHODOLOGY
Need for the Study
Formulation of Objectives
Literature Review
Identification of Grade Separated
Intersections
for Study
Data Collection
Performance Evaluation of Grade
Secondary
Survey
Accident andtrafficcomposition data(3 years before
Primary Survey
Traffic volumecount andComposition
Speed
Delay
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STUDY AREA (I)
STUDY INTERSECTIONS
The study intersections are selected in Chennai city area. Five grade separated
intersections are selected based on the form and shape as follows
IIT Intersection
Royapettah New college Intersection Royapettah G.H Intersection
T.T.K Road Intersection.
Data Analysis and Findings
Comparison with IRC Standards
Evaluation, Recommendations
and Conclusion
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Estimation of Delay cost
Delay is a common phenomenon occurring at signalized
intersection. Seldom one passes through all the intersections without
delay of atleast few seconds. Delay at a signalized intersection means,the average delay caused to the vehicles at the signal due to various
factors like traffic flow characteristics, vehicle type, timing of signal
phases and cycle length. Delay is estimated in this study using three
methods namely manual stopped vehicle count method, Websters
model and TRANSYT12 for the non peak hour and the best among the
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three methods is selected. For the peak hour delay is estimated using
Websters model and TRANSYT12
3 Estimation of Fuel cost
The queue length occurring at the intersection and the average
speed of vehicles in the queue was observed. Substituting the speed and
distance in TRRL fuel consumption equation for two wheeler, car (old &
new), bus and auto rickshaw (Eq 3 to Eq 7).
Two wheeler = (3.38+ (549.57/Speed) +
(0.00436*speed*speed))*distance -- (3)
New Car = (21.85+(504.15/Speed)
+(0.004957*speed*speed))*distance -- (4)
Old car = (10.31+(1675.52/speed)+(0.0133*speed*speed))*distance
-- (5)
Bus = (32.97+ (3904.64/speed)+(0.0207*speed*speed))* distance
-- (6)
Auto = 2*((3.38+ (549.57/speed)+(0.00436*speed*speed))*distance)
-- (7)
The fuel consumed per hour for various categories of vehicles
was found and multiplying it with present fuel price and delay per hour
for various categories of vehicles, the total fuel cost consumed was
arrived. The fuel cost was estimated for the complete year assuming
conditions similar to peak hour will be prevailing for 6 hrs in a day and
for 5 working days in a week.
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4. Compilation of Accident Data
Accident data was collected for 3 years before and after construction of grade separator.
Accident data was collected such that it has different types of accident data like fatal, grievous,
simple injury and no injury. Accident data for the study intersections was collected from Chennai
City Traffic Police.
5. IIT INTERSECTION
IIT intersection grade separator was constructed in the year 2000 with a cost of 7
crores. The length of the grade separator is 511 m. IIT intersection is a T-junction with the
grade separator segregating the straight traffic flow. Traffic flow is one way, from Raj Bhavan
towards Madhya Kailash. Volume count survey was done at the
intersection. The Fig 4.1 shows the arm wise flow at IIT Junction.
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Fig 4.1 Arm Wise Flow at IIT Intersection
The total peak hour flow at the intersection was 13535 Pcu
per hour. The peak hour volume flow through the grade separator was
1741 Pcu per hour.
Table 4.2 Delay Estimation before Construction
of IITGrade Separator
Capacity Analysis
Easte
rn
Arm
Weste
rn
Arm
Northern
Arm
Adjusted flow rate, v (Pcu/hr) 5056 5093 2212
Timing
G 41 41 26
Y 4 4 4
Width of approach road 10.5 10.5 7
Saturation flow rate, s (Pcu/hr) 5513 5513 3675
v/c ratio arm wise 2.68 2.70 2.78
Delay in Sec/Pcu using
Websters 313 341 92
Delay in Sec/Pcu using
TRANSYT12 147 156 99
Table 4.3 Delay Estimation after Construction of
IIT Grade Separator
Capacity Analysis Eastern Arm Wester Northern
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n Arm Arm
Phase I Phase II
Straig
ht
Right Right
and
Left
Right and
Left
Adjusted flow rate, v
(Pcu/hr)
3485 1782 1398 2999
v/c ratio, X 1.33 1.90 2.66 3.31
Delay in Sec/Pcu
using WebstersModel
119 151 102 231
Delay in Sec/Pcu
using TRANSYT12
43 93 110 138
Table 4.8 Accidents Occurrence at IIT Intersection before andafter Construction of Grade Separator
Type ofAccident
No. of Accidents
During (1996-
1999)
before
construction
During (2001-2004) after
construction
Fatal 6 3
Grievous 26 19
Simple 25 19
Non-Injury 3 3
Total 60 44
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Source: Chennai City Traffic Police
The total cost of delay and fuel cost before construction of IIT
grade separator was 367 Lakhs per year (Delay cost - 345 Lakhs, Fuel
cost 22 Lakhs). The total cost of delay and fuel cost after construction
of grade separator was 179 Lakhs per year (Delay cost - 173 Lakhs, Fuel
cost - 6 Lakhs).The savings was 188 Lakhs per year.
6. ROYAPETTAH G.H JUNCTION
Royapettah G.H junctiongrade separator was constructed in the year 2000 with a cost
of 8.5 crores. The length of the grade separator is 540 m. It is a four arm intersection with the
grade separator segregating the straight traffic flow. Traffic flow is two way.
The total peak hour flow at the intersection was 6733 Pcu
per hour. The peak hour volume flow through the grade separator was
1070 Pcu per hour. Arm wise flow at intersection is as shown in Fig.
4.3.
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Table 4.4 Delay Estimation before Construction
of Royapettah G.H junction Grade Separator
Capacity Analysis EB WB SB NB
Adjusted flow rate, v
(Pcu/hr)
199
31957
135
4
161
6
v/c ratio, X 1.40 1.38 1.27 1.51
Delay in Sec/Pcu using
Websters Model67 66 67 71
Delay in Sec/Pcu using
TRANSYT12
92 79 72 118
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Table 4.5 Delay Estimation after Construction of RoyapettahG.H junction Grade Separator
Capacity Analysis EB WB SB NB
Adjusted flow rate, v
(Pcu/hr) 744 996211
7
187
3
v/c ratio, X 0.73 0.97 1.49 1.32
Delay in Sec/Pcu using
Websters Model 54 51 63 58
Delay in Sec/Pcu using
TRANSYT1254 57 84 71
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Table 4.9 Accidents comparison before and after construction
of grade separator at Royapettah G.H junction
Source: Chennai City Traffic Police
The total cost of delay and fuel cost before construction of Royapettah G.H junction grade
separator was120 Lakhs per year (Delay cost 112 Lakhs, Fuel cost 8 Lakhs). The total cost of
delay and fuel cost after construction of grade separator was 83 Lakhs per year (Delay cost 80
Lakhs, Fuel cost -3 Lakhs). The savings was 37 Lakhs per year.
Type of
Accident
No. of Accidents
During (1996-1999)
before
construction
During (2001-
2004) after
construction
Fatal 6 3
Grievous 21 12
Simple 21 18
Non-Injury 2 0
Total 50 33
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7. ROYAPETTAH NEW COLLEGE JUNCTION
Royapettah New college junction grade separator was constructed in the year 2000 witha cost of 8.5 crores. The length of the grade separator is 502 m. It is a four arm intersection with
the grade separator segregating the straight traffic flow. Traffic flow is one way from Royapettah
G.H towards New College
The total peak hour flow at the intersection was 5184 Pcu per hour. The peak hour
volume flow through the grade separator was 834 Pcu per hour. Arm wise flow at intersection is
as shown in Fig 4.5.
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Table 4.10 Accidents comparison before and after construction
of grade separator at Royapettah New college junction
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Source: Chennai City Traffic Police
Type of
Accident
No. of Accidents
During (1996-
1999)
before
construction
During (2001-
2004) after
construction
Fatal 6 4
Grievous 24 13
Simple 28 14
Non-Injury 4 1
Total 62 32
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8. TTK ROAD JUNCTION
TTK road junction grade separator was constructed in the year 2000 with a cost of 10
crores. The length of the grade separator is 610 m with two four arm intersection namely TTK
road, C.P Ramaswamy road and Eldams road junction and TTK road and Luz Church road
junction with the grade separator segregating the straight traffic flow from TTK road to C.P
Ramaswamy road. Traffic flow is one way through the grade separator
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Volume count survey was done at the intersection. The peak hour flow at the
intersection was found. The total peak hour flow through TTK road and Luz Church road
intersection was 5076 Pcu per hour. At TTK road, C.P Ramaswamy road and Eldams road
junction was 6609 Pcu per hour. The peak hour volume flow through the grade separator was
2355 Pcu per hour. Flow through grade separator is one way from TTK road to C.P Ramaswamy
road. Arm wise flow at intersection is as shown in Fig 4.7.
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Table 4.6 Delay Estimation before Construction
of TTK road Grade Separator
Table 4.7 Delay Estimation after Construction
of TTK road Grade Separator
Capacity Analysis
TTK road, C.P
Ramaswamy road
and Eldams road
junction
TTK road and Luz
Church road
junction
EB WB SB NB SB EB NB
Adjusted flow rate, v
(Pcu/hr) 20
5497
419
3
298
5
171
4
136
2
235
5
Delay in Sec/ PCU
using TRANSYT1270 65 76 78 86 69 48
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Table 4.11 Accidents comparison before and after construction
of grade separator at TTK Road junction
Source: Chennai City Traffic Police
Capacity Analysis
TTK road, C.P
Ramaswamy road and
Eldams road junction
TTK road and
Luz Church
road junction
EB WB SB NB SB EB
Adjusted flow rate, v
(Pcu/hr) 205 497 4193 825 1714 1362
Delay in Sec/ PCU using
TRANSYT1252 58 72 59 36 40
Type of
Accident
No. of Accidents
During (1996-
1999)
before
construction
During (2001-
2004) after
construction
Fatal 4 6
Grievous 30 19
Simple 28 14
Non-Injury 3 2
Total 65 41
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The total cost of delay and fuel cost before construction of TTK road
junction grade separator at TTK road and Luz Church road junction
without grade separator is 79 Lakhs per year (Delay cost 74 Lakhs,
Fuel cost 5 Lakhs) and at TTK road, C.P Ramaswamy road and Eldamsroad junction was 123 Lakhs per year (Delay cost 115 Lakhs, Fuel cost
-8 Lakhs). The total cost of delay and fuel cost after construction of
grade separator at TTK road and Luz Church road junction was 28 Lakhs
per year (Delay cost 23 Lakhs, Fuel cost 2 Lakhs) and at TTK road,
C.P Ramaswamy road and Eldams road junction was 81 Lakhs per year
(Delay cost 78 Lakhs, Fuel cost -3 Lakhs). The savings was 98 Lakhs
per year.
9. Conclusion
The savings in delay and fuel cost after construction of IIT junction
grade separator was 188 Lakhs per year.
The 21% reduction in accident was observed at IIT junction after
construction of grade separator.
The savings in delay and fuel cost after construction of Royapettah
G.H junction grade separator was 37 Lakhs per year.
The 37 % reduction in accident was observed at Royapettah G.H
junction after construction of grade separator.
The savings in delay and fuel cost after construction of TTK road
junction grade separator was 98 Lakhs per year The 32 % reduction in accident was observed at TTK road junction
after construction of grade separator.
In planning stage itself future modification in the grade separator
should be considered.
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